I think someone in the secret police, posing as a tourist with a camera would be rather easy to spot; they're not getting harassed/followed by the secret police
It's even easier than that for those who are not the target of surveillance...
I've mentioned this befor on this blog but it never hurts to refresh peoples minds on such things :-)
A number of years ago I had "occasion" to frequent parts of London near New Scotland Yard, the MI5 and MI6 buildings and a number of the places they had as "innocent businesses" etc.
Some of which were used for training in "field craft" part of which is to follow someone...
Well whilst it is not always easy to spot the "mark" it is usually trivialy easy to spot the person following them as they realy do stand out like the proverbial "fish out of water".
The reasson is they are concentrating to hard on the "mark" and trying to look inconspicuous to the mark. The result is their body language and behaviour is totaly wrong for being "in the crowd".
You can find a nice quite cafe and sit with a friend over a lazy tea/coffee or lunch and play "spot the numpty" or as they might prefer "spot the officer in training".
Once you have spotted them you can usually spot the "mark" who generaly does not stand out as they are "a member of the crowd" and behave like it.
Now for the important bit...
Nearly all people who follow others for a living or importantly for ill intent are no good at it and stand out like the proverbial fish out of water.
Those tasked with protecting Veeps/VIPs who realy know what they are doing have both the close support "bullet catcher" body guards and also those unknown to the VIP (and most of the close support team,) who's sole job is to watch for who is watching the watchers / bullet catchers. They have liason with the senior body guard or others who's job is "to run interferance" on those paying to much attention to the close protection team. Including "tagging and bagging" where required.
Being good at surveillance on people is a hard won skill and takes much practice, because whilst it's hard but by no means impossible to remain unknown to the "mark" remaining unknown to trained observers you cannot easily spot is very very difficult. Thus the often used way is to have a team who "forward follow the mark" and "tail the tail". They move backwards and forwards of the mark and change between the various positions in fairly short order. The usual running is to get forward followers drop back slowly on the mark to form the tail and then drop back to tailing the tail looking for those who might be watching the tail. They will then move forward of the mark (by car etc) again and drift back down onto them. A well trained team of five or six people can thus follow even a quite wary mark over any reasonable foot journey.
If you want to avoid being followed and know the lye of the land fairly well, being sufficiently fit to get a push bike up to speed in conjested roads and down alleys which come out in places difficult for cars to follow causes significant problems for those following in the past. They either had to use the same transsport that makes them realy stand out, or call in air surveillance such as a helicopter the presence of which wold be fairly easy to detect due to rotor noise.
Sadly the use of light weight surveillance UAV's which are both small and light and thus quite quiet has made the "marks" job much much tougher.
The solution is to get under cover and use a heat shroud and heat decoy. The shroud comes in a number of forms but basicaly reduces or eliminates the "heat signiture" of the person wearing it and the heat decoy puts out a heat signiture just like a human. Thus if done correctly all the circling UAV sees is the marks initial heat signature fade into the decoy heat signiture and misses the now masked marks heat signiture move away from the decoy.
Importantly remember about the likes of smart phones and other active electronics that can give you away.