When sneaking past security to infiltrate a bad guy’s fortified compound, my mode of covert subterfuge would have to be the often underused yet effective…walk through the front door disguised as the telephone repairman ruse. 
It consists of the following:
- Thick black-rimmed glasses
- Goofy smile
- An air of indifference to whatever evil plot is seen or overheard while in the presence of said bad guys, while pretending to fix a fully functional telephone receiver
- Helpful prop would be a tool belt while holding at the bear minimum, a few handy telephones, in best case scenarios, a nifty screwdriver
- No telephone ID’s needed, as the best infiltrators can just talk their way through security
A good example would be Bruce Lee in The Chinese Connection (Fist of Fury) 1972. You can see the scenes in this clip, starting at 2:09.
https://www.youtube.com/watch?v=SFghe514COY
An effective use of the disguise can also be seen by Kurt Russell in Big Trouble in Little China, 1986, twice when he infiltrates the brothel and later with telephone in hand at the lair of the bad guy, Lo Pan.