It's a GPI (Gaming Partners International) mint mark, though I haven't seen that "shield" version before. Perhaps it is because this 2015 series was all done on a HOUSE mold, not a H&C mold.
The GPI mint mark I'm familiar with is the GPI inside a "box" like this:

The reason I'm confident it's GPI is this:
There's a whole series of CC-Reno chips done in 2015, and on the NGCB approval list for January 2025 ($1, $5, $25, $100 and a not-shown on ChipGuide $500 too). Interestingly, the 50c lagged behind, not approved until March 2015.

All but the $1 have the same "shield" mint mark worked into the inlay graphics if you look closely on their pics on ChipGuide. As example, here's the $5 from that series along with the 50c chip you show (pic from ChipGuide):

This series of chips is on the "Chip & Token Historical Report" on the NGCB website if you scroll down far enough. And these chips are also on the 2015 alternate list that I wrote about in the "Decade..." article in a recent CCA magazine. That approval list version also includes a column naming the manufacturer, which says "GPI" for this whole series of HOUSE mold CC-Reno chips.

Good catch, by the way. I find mint marks interesting (both tokens & chips), but I hadn't caught this one till you pointed it out.