This is intended as a supplement to mhoran_psprep's answer.
For small companies, you can go to local/state department of labor. They're able to provide you with the assistance.
The most important thing is to seek help and advice asap. Don't "Let it be". Everybody has this civic duty - you're a citizen.
Before you report it to the right channel, document it. Record the time, place, the event and the inappropriate remarks.
Added after OP edited the question in case others may run into similar situations:
In response to what OP says "it's about a group that is not visually identifiable". It would be a tough call whether to report it or not. I think the action depends on the nature of those remarks and the extent of them. I am going to make up the following scenario: suppose you like to wear red color dresses and your co-workers say you look prettier in green. It's hard to report this to HR or other channels. In this case, you need to ask yourself a question, would the situation impact your job performance? If not much, you can ignore those remarks and move on. That's not to say you accept those remarks. Rather, you should concentrate on your job. However, if your job performance is seriously impacted by those remarks, you need to do something about it. Your job is the most important thing when you're in your work place. The most important thing in your work place is the preformance of the work team. Somebody needs to make sure the whole team is doing great to generate profit for the company. Otherwise, why pay the employees to be there? For them to make remarks?