The dress code issue is a red herring.

We've been round and round on this before, but there's no way for two or more feds to remain covert/undercover/unknown in such a small arena. Airplanes just aren't very big. F cabins are really small places to try to blend in. Frequent flyers generally know many of the indicia of the marshals' presence. It just doesn't take a rocket scientist to generally be able to pick them out.

And since most people agree that even terrorists can become frequent flyers (and the brain trust at the TSA even assumes that Frequent Flyers are likely terrorists), it isn't a very big leap to assume that the terrorists can probably spot the sky marshals as well as I can.

Let's look at just one indicia: Reasonable people can probably all agree that alcohol and firearms don't mix. So a prohibition on armed LEOs consuming alcohol probably generates uniform support. So when 14 out of 16 F pax order alcohol on a late afternoon/early evening flight out of a business hub, the two who don't drink stand out. Especially when all other factors are considered: Aisle seats (never windows), often across from each other. Add the age (no elderly marshals, and no 19 year old marshals), the hair, the clothing, the pre-boarding (I was the first ticketed non-marshal pax to board and they were already seated), the cool PDA, etc., and there's really no way to stay undercover.

In an arena? Sure. On a busy street/sidewalk? Probably. In the airport itself? Sure.

But in such a small, confined space? The 8-24 seat F cabin? You've been spotted.

Perhaps not every time. But terrorists don't require 100% accuracy in figuring out who you are; each time you've been made you are vulnerable.