Trying to add image to signature - tells me invalid HTML

[mikedboh]

Trying to add a card image to my signature but when I enter the HTML for the image it removes it and says invalid HTML.

Is there a special way to add images to the signature?  Do I have to use photobucket or can i host the image on my own server?

Thanks

[mikedboh]

Also could a mod please add the silver spade to my sig??

<img src="http://i.imgur.com/Gfc4B.png" border="0" width="40" height="40" align="right">

Here is a link to the photo I am trying to add to my sig.  Is it too large?  
http://s10.postimg.org/gaxvj3tt5/credit_card_sig.png

[mikedboh]

thanks