>Tuna Fish is part of the vernacular, I'm afraid, as is Cod Fish.

That just adds cod fish to my list as another example of redundancy. But interestingly cod fish doesn't seem to show up on menus as often as tuna fish does.

>But PIN and VIN are generally said as a word, so I guess people want to distinguish between a pin (a piece of metal with a pointy end) and a PIN by putting the 'number' after it.

I guess saying "Use your PIN" to someone standing in front of an ATM could be confused as meaning the small pointy thing rather than the personal ID number you were issued for the ATM, but then that might represent an even bigger problem with the person to which one is speaking.