Yeah, at some angles a P-47 looked a lot like a FW-190. As the Baron says any little bit of ID helps when dealing with twitchy Allied AA gunners.

rooster513

So I've been doing some research for P-47D builds I have coming up and have noticed many pictures of the underside that have insignia on both wings. Yet when I look up decal sheets alot of them don't depict this. Was it standard for insignia on both wings? I just find it interesting being alot of other types of planes in that era had them only on the one wing once they switched to stars and bars.  

Those were additional insignia added locally for indentification purposes, for units engaging in ground attack.  I know that they were applied in some cases in the Mediterranean theater, in Italy, and as far as I know, the additional marking was just added underneath, not to the top right wing.

One of Lt. Frank Klibbe's "Little Chief" versions also had the additional underside national marking, so it must have been done in the ETO, too, for aircraft flying from England.

I don't think that particular in-theater marking has any connection to the general specs defining the national markings for USAAF aircraft, though.

Officially, the USAAF were ordered to remove insignia from the upper right and lower left wing in February 1943. Like most such orders, it would take some time for that change to be universally implemented, and it might even vary from unit to unit in the same area. Broadly speaking, it was far more important to keep planes up to strength in combat, than to insure they were perfectly marked according to regs at the exact hour an order went into effect.

As always, real photos are your best guide.

There's a nice rundown of changes here