Looking in Scott Catalog there are only two watermarks listed for this particular stamp. A large star and a small star. This stamp has a crown watermark that doesn't match exactly the crown watermarks listed under Great Britain.
Image below more accurately reflects the color of this stamp
Retroreveal image is more revealing
The horizontal lines in the crown do not match what is found in Scott. I have read other threads regarding forgeries of this issue. The crooks didn't forge watermarks also, did they?