Let's put this into context : I have to go somewhere during 5 minutes, right? So I godmode because the spawn throws you out of it, (I mostly play on the surf server) and I don't especially like being loopkilled. When I come back, I forget that I have godmode on until a pyro tries to set me on fire.
I ain't the only victim of this though, and if you have the godmode command, it probably happened to you more than once. Don't lie.
Anyways my idea was that when you have godmode toggled, there's text at the bottom that says something like "Hey, you're still in godmode!". I dunno it's just an idea.