Signature parsing - where to hook in

[Lincoln]

My board uses dynamic signatures that use Javascript (for Folding@Home point totals if you're familiar with that project). Members create these sigs with a generator page.

I'd like the generator to instead dump the created sig into a new database field for each user. Then, I'd like members to simply put [sigtag] (or whatever) in their signature and have the board replace it with the code they made in the generator.

I'm fine with putting the code in the database, but I can't find where it would be best to parse the signature (remove the tag and insert the custom sig).

If possible, I'd like to disable Javascript in signatures but have this hack still work (i.e. have it parse after any checks for Javascript).

I'm not looking for someone to code this for me, just a point in the right direction of where I could/should insert this code or plugin to do the parsing.

Thanks! :D