The earlier answer by @svj carries high validity for coming from Indian women's point of view. I am Indian myself and understand your situation very well indeed, though only from men's perspective. In fact I just recently asked (and answered) a question here on how my unmarried sister can convey in a prospective job that she is not "available" for an "office romance." The boss was alleged to be womaniser in that case.
Your main objection to those men's behavior seems to be the double standards involved in that, in an identical situation, the men were "respectful" with your female colleague, looking away because she was married, and outright nasty disrespectful with you (staring and giggling like schoolboys) because you are an unmarried woman they consider "available." If that was not your reason then please edit Q to clarify.
Sad but true, that double standard is entrenched in this society and also in many other cultures worldwide. Since the married woman is considered sexually "unavailable" in India by social taboo, those men probably did not want to "inflame their senses" in a hopeless cause. Moreover she could have insulted them loudly if she caught them staring and her husband could have thrashed them even at risk of breaking the law: both acts would be considered a justified reaction by most people simply because she is a married woman.
Married women are "respected" in India not only because disrespecting married women invites severe social punishment, but also because Society wants to condition women (and men) to see "married" as the ideal state and thus make unmarried women aspire to the married state. It makes it easier for patriarchal society to control women, though feminism is still not popular here. Unfortunately the negative form of reinforcing this social conditioning is to make unmarried women insecure by treating them disrespectfully as "available till married."
3. Futility of Discussion
So you are fighting established social stereotypes experienced by millions of women. The difference in those men's behavior with married and unmarried women is not even worth addressing with them because they seem stupidly insensitive from your description and probably wouldn't understand what you are trying to tell them. They don't respect the married woman; they just want to avoid complications. You also risk wasting your psychological energy trying to make them feel your sense of injustice that you are not being "respected as much as a married woman", when in fact you deserve the utmost respect as a woman and there is no real way to interpersonally communicate that to a man who does not respect women in the first place.
4. All That Remains
All that remains is to assess whether their behavior towards you specifically (ignoring how they behaved with the married woman) could be described as "sexual harassment at the workplace" or even "conduct that outrages the modesty of a woman" which are punishable offences in India. Next time they do it, you can make that assessment and decide whether you want to file a complaint either with your superiors or with a legal entity. Note that the law does not differentiate between married and unmarried woman because it is discriminatory to have such a difference.