Can I make a signature on the ASC?

Yes, but you still have to upload images every time using the Camera icon in the message window's toolbar. However, you can construct a signature you want and then simply do a screen capture of it. That way you only need to upload the image of the signature.

If it's possible I can't help you. So far there seems not to be a simple way to script an action to post a signature because the ASC mandates that we can only include images using the Camera icon method. No more links to display an image like we used to do.

It is old fashioned, but we don't make the rules or their BBS software. It's mostly a security issue for them. Uploaded images are scanned. But posting image links to remote servers makes it too easy to communicate malware.

I think after you upload it once, you are able to copy and paste the already-uploaded one within ASC. Give it a try.