Limiting Sign-ups on a Form

[zomgWebdesigner]

I need to make a sign-up form that can only have a certain amount of sign-ups...otherwise...there are only 30 physical spots for the activity and I can't allow more than 30 to sign up on the online form.
How would I do this? :eek::confused:

[abduraooft]

How do you count a single "Sign-up" process in your system?