Bummers can be funny. I like the idea. The sign does not look right, no dimension to it.

Fantastic idea author...super cool thinking...IMHO u should work a bit more on a sign to give more realism there...everything else is well made...best of luck

The sign is being problematic for me...I tried adding some shadows, and it looked even more "fake" (like the rest of the image is SOooo realistic!)...

Any suggestions on how to improve the sign would be most welcome!

hmmmm...maybe instead of white frame u could use some a bit rusty metal texture and create frame with that....if u do that u have to create shadow in frame too...also would be cool to create some detaching parts on the surfer poster to achieve casual look...this is just and idea author...GL

You can try duplicating the sign author and just distorting it so it look 3d... wish I could help, but its not something ive done yet. Otherwise try adding some noise and a bit of an off white colour to the poles... Better yet the chances of it having some rust on it from being close to salt water

Other than that, its funny

Your main problem IMO is that the frame is all one color, the main surfer has an orange sunset glow on his back so that same light will cast a slight burned shadow at the back of the sign (on the sand) and an orange to black gradient overlay at very low opacity on the sign will give it more realism. Hope that helps.