I tried it with my logo in the signature and tested it on Hotmail, GMX, Gmail and my old office Outlook based account and it didn't show in any of them.
If I remember correctly I eventually got it to show in some of them but the formatting was all out and it didn't look as good as it did on my computer so I gave up!
If anyone wants to send theirs to my Hotmail account just send me a PM and I'll give you the address, I'm interested to see what they look like. :)
I'm pretty sure the method I linked to above results in an HTML based signature. You design it in Word but can also use Frontpage or similar programmes.