Basically: Not really, unless they're pretty sloppy and don't counter your Astral Tracking. Although spirits might not be as unstoppably dangerous as you think.
Any spirit influencing material matters will leave a material trace, just like any physical being - because they must materialize to affect the material world.
If a spirit wants to affect anything on the physical
plane, it has to materialize first (p. 314). It gets physical
attributes based on its type (Spirits, p. 303) and appears
as a solid, physical version of its astral form—it’s relatively
solid even if it doesn’t look solid, like a spirit whirlwind
or a water elemental.
The spirit is going to leave some kind of physical trace at the scene, and an astral impression wherever it travels. That will fade relatively quickly though, and the mage can wipe it clean - so you're right, it is quite a challenge to track a summoner who wants to stay hidden when you arrive on the scene way too late. Just as it would be hard to track down a Rigger who used a sniper drone, or to find a decker who stole your files, or to find a sneaky assassin, 8 hours after the event when they've covered their tracks.
You do, however have Astral Tracking to fall back on if the mage hasn't erased their tracks everywhere the spirit has been.
Furthermore it seems to me that the astral signature vanishes with the spirit.
I'm not seeing where that's the case in the rules. You've even got a "+1 for every hour since the link was active" mod in the tracking threshold table (p315), which indicates you can track stuff that happened in the past after the link is gone as well as things that are happening now. If a spirit was there 4 hours ago, for example, this would suggest you can trace its origin at a +4 threshold (and tracking master by spirit is a +0 modifier for bound spirits, or +2 if it wasn't bound).
On the theme of danger...
A nonawakened person is pretty much helpless against a spirit
This isn't necessarily the case.
The materialization thing means that even unawakened victims can defend themselves quite effectively. Once the spirit materializes to make its assault they can physically attack it just like any metahuman opponent. Spirits do have all manner of freaky powers, and can more easily sneak up on the unawakened, but they still go down if you pump them full of bullets. Even before they materialize you've got a chance of spotting them:
Physical beings may sense when an astral form passes
through their aura. Make a Perception + Intuition
(4) [Mental] Test—you receive a +2 dice pool bonus if
you’re Awakened. If the test is successful, the character
feels slightly breathless, and they experience a chill or
tingling sensation from the passing of the astral form.
Security personnel are trained to recognize this feeling
as a sign of an astral intruder.
Dangerous, yes, but not really any more so than other sneaky backstabbers who might try to kill you.
Let them
No seriously, let them.
They want to keep the McGuffin of doom, the schematics to the bank that the Johnson asked them to get, the sacred Rhino of the city?
Let them keep them.
They're seriously writing plot for you right here, don't speak to them as a GM saying "If you do that, X..." they're experienced runners now; this is fine at the start of games when players are learning systems, but when they know the world more, they've done a few runs - they need to expand out and be let free from the cotton wool of GM warnings.
Give them an OOC 'the talk' before the next game; "You're experienced runners now, what you do is up to you, what happens will happen as a consequence of that, so think carefully about stuff before you do it."
You can still give them warnings that their characters know about, if they wouldn't think of...
"Hey Street sam, you know for a fact from your street contacts that holding onto a jacket from the DOOM X bikers gang is a way to get the gang hunting you down. Just so you know."
Why letting players keep stuff is great for your game
- It puts the players more in control of the game, makes them feel like there is less railroading and hell, they get to keep stuff! They like that stuff.
- Consequences. Oh such a beautiful word. Where the hell would they keep the sacred Rhino? If they keep the schematics of the bank what are they going to do with them? If they don't hand them over or the McGuffin then they might get a group of people coming after them. And for this formula? Well, they can use it. They could sell it. But if they've got it then the person who hired them is still going to want it. Bad enough to hire people to take them down, or, y'know extract it from their bodies with a syringe...
- Or so they've got the schematics for the bank, they can try and crack it themselves, they're giving you plot hooks! They've got a rhino; okay, so how are they going to get the half tonne of specialised rhino food every day for the thing? And think of all that lovely rhino dung that they get to pick up ;)
Rep is great, it gets you off the hook; but like stocks and shares, it can go up and down. If they start doing Jobs for their Johnson and not finishing as required, then the next one will be a bit harder to do, the pay less... and so on.
Let them keep the stuff. Really.
Don't say anything. Well maybe just...
Player: Screw the Johnson, let's keep this Sabre-X missile launcher, it's awesome.
Other Players: Hell yeah!
GM: ~smiles to themself~ ~writes something down~
They'll learn to fear that smile ;)
Best Answer
The reflex adjustment you pay for typically includes mental acceleration. This doesn't just boost your Reaction, it gives you more IP. Hitting someone on accident is not really a reasonable problem, nor is spilling food. Constantly interrupting people because they're going to slow, being frustrated at how slow one's one body moves, taking 'shortcuts' that shave seconds off of routine tasks like moving a fork into one's mouth but look really weird and sometimes spill food everywhere, these are the kinds of issues you get from wired reflexes. It's not just your body, your mind is moving faster too. Most runners who use them only turn them on when necessary, which works fine once their on; there isn't really much of an 'adjustment time' needed: if you've any of the latest FPS games you're probably familiar with moving in slow-mo which is basically what happens when the reflexes are on. The main disadvantage of doing this is that you might not have time to turn them on in certain situations (e.g. an ambush) before it's already too late. Also they make you physically better with basically no drawbacks at almost any task, which makes using them desirable, even if it's mind-numbingly boring.