More subtle indications such as:

The door to where you practice is locked and no one answers the doorbell at your pounding.

Everyone else has a mic but someone forgot yours.

All your hear is a dull roar from the monitor.

Everyone else is playing in a different key than you are playing.

Someone's cat did something rude in your instrument case.

All the seats are taken in the van and you get to ride strapped on top, and it's raining.

All the other members of the band head for the loo when it's your turn to lead a song.

After the gig is over the rest of the band takes off in the van without you...

Cheerily,
Charley Noble