Are you trying to differentiate between a registered and unregistered trademark? From what I understand, to get an unregistered trademark, you must add "TM" to your mark. That type of mark is mainly valid in the region/state that you're doing business out of.

To get a registered trademark circle r (R), you must file the right paperwork and pay a fee with the federal gov.

In both cases, to maintain your trademark, you must clearly show that it is your trademark with either a TM or a circle R (R). There are other requirements but these are the two I was looking for when stating that there is no YC trademark. If they do have a trademark on the Y with orange background, it's being maintained poorly.