there's no reason for your signature options to be blocked, that I know of.
When you go into your User CP page, and click on Edit Signature .... what do you see What options are available for you ??
You do know that you have to have pictures downsized to a certain size limit ... pictures may have to be on a website or hosting site ... you have to copy/paste the IMG address of pictures into your signature box.
Are you having trouble with the size of the picture you want in your signature ... or is it that you can't figure out how to copy/paste the image address ... or do you just not have signature posting/editing capabilities available in your User CP ??
I'll be back on late tonight, and I'll check back and see if you've been helped already ... if not, I'll address the problem as best I can, given whatever info you're able to provide. If that don't work, there's always another option --- send a PM to "Slab" (Ed - site owner/admin) and explain it to him, and let him fix it (if something is amiss) or explain how you can go about fixing it.
... hang in there, we'll get it sorted out
... cp