Spotted this one on a sticker the other day, it's the logo of an online clothing shop.

This is a t-shirt design (who would've thought?!); from the description on their website:
"This head hunter inspired design puts headhunter tattoos, spears, barongs, fertility symbols, skulls, swords, shields, and axes to piece together the Skull-&-Bones."

I've seen this one being used for various purposes.

The above design is used by a clothing company for... you guessed it: T-shirts.

No collection of skull and crossbones variations is complete without Hello Kitty and crossbones.

Spending all your money on diamonds and fancy shirts will leave you with no money for food and you might end up looking as hungry as this young lad does.

A radio station called Radio Free Texas uses this on a T-shirt.

A skull decorated with typical witch hat and nose. Plus two crossed brooms below that. Done.

We all knew this one would come, right? Way too obvious. Who cares.

Ok, so this one is the classic symbol we all know. I consider the above image the most prototypical version of the skull-and-crossbones symbol, thus all variations are more or less derived from this.