Going by the example of that theater that showed an original 35mm print for free before they closed down several years back, you’re probably safe. And they certainly didn’t keep it unadvertised.
On the other side of the coin, there was a bar that got into trouble showing the OT on video, probably because they had paying customers, (buying drinks) or they did it too many times. So just don’t pocket the concession money or anything. 😉

Any experts on the legality of such a thing feel free to chime in though.