Well, I did that one with photoshop... but you can do it in paint. Just cut out the picture of your dog/dogs and put them on one single paint page (just do the select box or lasso around the portion you want, cut/copy, and paste onto new paint doc.) First, on paint, you would color your background. Then you can use the text box to type whatever you want. Then you save. I usually save as a PNG because JPEGs get blurry after you save them for some reason. (At least for me) Upload it to photobucket. Copy the code that starts with [ I M G ] just not spaced out... then here...

Go to user CP upper left corner. Then edit signature. Place in box and hit okay!