Haha, I was going to mention the chances of running into an officer of a country we don't identify being low...but I sadly did not. Foreign branches can be very tough. I ran into an officer of a an island nation...had two stripes on his shoulder boards but a gold oak leaf...luckily all of those still were higher than the white shield collar devices I was wearing, so a salute was rendered.
Cross-branch saluting can be pretty tough, especially if you don't know where to look on the uniform. The crows on the collar devices of Navy cammies look alot like a full bird...luckily you can factor age into it. The only time I've been a little angry about a missed salute was on a Navy base in Virginia, in which the sailor obviously disregarded it as a slight for the branch...but that was one bad apple. In general, it isn't too hard for anyone to pick out. To tell you the truth, I feel bad for the non-sea service members, the stripes on our sleaves can been pretty tricky.