Most people don't have an understanding of the rules of Gursikhi. However there are certain societal 'norms' if you will, including a common one that an external indicator of a married woman is sindoor and manglsuttur. Since these are commonly understood visual signals, it doesnt matter whether you live in Kerala or Kashmir - you know what sindoor/manglsutur indicates.
At the end of the day this is an entertainment program broadcast around the country and indeed the world, and to get the message across they have to use things that the average indian understands ie. you may not have a clue about the program, sikhism and if you just watched yesterday's episode as your first one, you'll know that Geet is a married woman just looking at her.
Going back to MMDR - I think they've done a fairly good job of being respectful to the tennets of Gursikhi (the religion), unlike some of the other dramas on telly at the moment. The other things such as the sindoor etc are cultural/societal rules that are man made... and not sikhism per se.