Titan Mercury provides funding to a lot of the RTCs, including the SERTC. That money goes to equipment (singlets, etc.), athlete/coach compensation, travel for training and competition among other things. I'm assuming that a part of their deal with the RTCs is that their name appears when guys register and (maybe?) get their USA Wrestling card.
That's why you'll see in brackets, for example, Hunter Bolen (TMWC/SERTC) or David McFadden (TMWC/Penn RTC). Sometimes folks will get lazy and just put Hunter Bolen (TMWC).