Who signs marriage license?

If you need witnesses (not every state requires it), it really could be anyone. Usually I don't even have the photographer take a photo of it. My personal feeling is that it's not that significant an honor or a snub. I usually have the BM an MOH sign it.

My state (Texas) didn't require it.

I would choose a sister (perhaps the oldest) since you're close.

Yep - depends on your state. Here in PA only the officiant signed it (we didn't even have to sign it - we only signed the application at the court house).

I am in Texas as well it was not required. Use to be but isn't any longer.

It depends, here in RI anyone two adults can sign it in NV it has to be two nonrelated adults you'll have to check your states regs

We are having my sister and his brother sign. His son is BM but he won't be 18.

VA doesn't require a witness signature, so no one signed mine.

California requires two.

Here in Alberta, Canada you have to have 2 witnesses. The MOH and Best Man signed ours.