To explain, in Team Fortress 2 there are 9 unique classes, each with their own character, appearance, and personality. Tails here is dressed as the Enginer, often referred to as "the engie". The engineer himself is extremely proficient with machines. Now do you get it?
You know I've always thought Tails would totally make a good engineer. It does fit him alot in a heck of many ways. [Like Sonic fits the Scout for obvious reasons, plus I would find it funny if Tails Engie has to put up with "the saying" all damn day] XD but anyway, it's an amazingly drawn picture and would be a good spray on TF2