As a past tense verb, which appears to be what you are looking for, it also means 'identified/named' or 'with tabs affixed'. It is also Special Forces slang for, in effect, 'marched', as in: "We tabbed 15 clicks yesterday."
Sorry, F, but I've never heard the word used in any of these senses! If I had to guess, I'd probably go for 'b', in the sense that someone has obviously been keeping 'tabs' on you before exposing your activities. But I have no idea really which is correct. I hope someone else comes along with a more definitive answer. Cheers