best way.
click on my albums (under the AHB logo top left, under your username)
click new album
click new image
add your image
go into folder
click image so its in the main window (not popup window)
right click on the main image and select copy link location
add this to your signature .
Or you could do the same in flickr and right click and select copy link location, But make sure you have resized it previously to a size that is user friendly