its a simple effect, but you should try learning how to blend in pictures, like..using the dodge tool or sumthing (im not a great artist at blending in either) i ussually use gaussian blur to make it look nicer, and then use a blending setting like overlay to blend it a bit in with the background
also you shouldnt use the simple color change thing (Ctrl+C) but you should use color balance (edit>adjustments>color balance, if im right) mess with the settings and u can get some cool things, last but not least, the famous...black stroke border, after you made your sig/artwork most ppl use a 1 px black border if the sig doesnt blend in well with the forums background color, just make a new layer, select all (Ctrl+A) and go to edit>stroke and add a 1 px border (black) on the "inside"