Signature or avatar. AFAIK signatures cannot be uploaded from computer like an avatar can. (I'll need to double-check upon that.) What you can do is host the file at a free hosting site. Google for free hosting sites. There's many. (oh but there is one that we don't allow on this site because it was popularly used by trolls/spammers.)

Also click on the FAQ button above as it does give some information on how to's of signatures. We allow signatures as long as they are not offensive or too large or against the Forum Rules. We don't allow advertisements to commercial sites.)

There is also an option to use a picture that is on your computer.

Download or save a picture onto your hard drive, then browse for the file location in LW User CP.

Good Luck

vBulletin version 3.6.1 has the option of uploading a signature from your computer so maybe this version does as well but it's just not activated.