A hat or cap is a popular souvenier.
Naturally, Segaworld of Sydney had several on offer. This is a rather bright green cap, with embroidered design. Sonic's head and torso are on the top of the hat, but his name and hands are on the brim. Interestingly, this stock-art like image has the mouth open, which is a bit unusual. It's made to look like Sonic's hands are 'popping out of' the brim, to hold the name/logo. Due to the construction of the hat, the hands are a bit far to look like they are 'attached' to the above torso, but the effect is still interesting.