On the wiki page for Squad, it says:
Squads are limited to 30 players.
In the past, when I've right-clicked on a commander's icon and selected "Join Squad", I didn't receive any visual feedback that I had joined. I now suspect that it's because it was full. Is there a way to tell whether you are in a commander's squad after trying to join?
Best Answer
Just click on the little right-arrow on the top left, i.e. at the top of your party info. There, you'll see options to invite players to your party etc. as well as whose squad you have joined. For instance, see the wiki's entry on Party and look at the top right image (it would show your squad commander instead of "Not in a squad" if you'd joined one).
However, being in a squad in no way forces you to "stick with your commander" or obey their commands, etc. (Please see Gwen's comment below.)