When using Glyph of Warding to store a spell, it gives the following restriction on what spells can be stored:
You can store a prepared spell of 3rd level or lower in the glyph by casting it as part of creating the glyph. The spell must target a single creature or an area.
On page 204 of the PHB, it says the following about spell targeting:
A spell's description tells you whether the spell targets creatures, objects, or a point of origin for an area of effect (described below).
Looking at those passages together, it seems like a spell with a target of self (for example, Fire Shield) would be a valid spell to store in Glyph of Warding as it targets only a single creature. As long as the Glyph of Warding was cast at 4th level or higher, I don't see any reason why that wouldn't work.
Am I interpreting the rules correctly?