Does anyone know if it's compound or not?

For example, say it was $250, and a penalty of 1% per month late. After four months, would it be:

250 * (1.01) ^ 4

or

250 + 4 * (250 * 0.1)

or something else?

The difference is negligible. It works out to be $260 total either way. I'd recommend calling CT DRS if you want definitive confirmation.

I'll shoot them a call tomorrow then.

I'm just surprised that it isn't clearer on the form.