" That is a theory. Unless a theory is tested it remains a theory.
Perhaps you should approach what turns out to be part of a civilian football team or a netball team and say"
There is no "theory " attached to TOFO's accurate criteria whatsoever.
The simple and salient facts are that service personnel do stand out when in civilian environments.
As I said in a previous post, when staying in a hotel in Southsea, this was 2009, I watched in disbelief as Shrivenham's less than intellectual elite all formed into little groups outside the hotel, to be "briefed" as to getting their taxi to Gunwharf, where to assemble thereafter and which eateries they would then visit. They all wore similar clothing as military personnel are prone to do which also adds to ease of identification.
I also said that, apart from potential terrorists, not everybody in the UK was supportive of the UK military, consequently, behaving the way they were drew attention to themselves.
Then there are the ubiquitous white people carriers which can be seen at Motorway services.
The moment the pax get out, or stand around, it's obvious they are military. They form groups through the nature of being military and I might as well add they also tend to talk to each other as if still on duty. Then they all head for McJunk / KFC etc....as a group.
In 2014, I was sat on a train going through Shrewsbury and the carriage was "treated" to the arrival of, presumably, members of the Royal Irish from Ternhill. The drinking had clearly long begun and the language was more applicable to a barracks plus, they were openly discussing whom they thought would be next for promotion in the SNCO ranks.
Dishforth services, late at night, stopped for fuel. At the next pump, an Army officer dressed in civilian clothes, albeit standard "off duty" wear for officers, a topic which has been discussed on here before. Again, stood out like the proverbial.
There aren't that many military locations left in the UK and terrorists are far from stupid, they tend to do their reconnaissance to gather intelligence about potential targets first.