In the news recently has been the work of protest projectionist who has been casting messages in light up onto the lintel of the Trump International Hotel, featuring the Emoluments Clause, the legend "Emoluments Welcome" and "Pay Trump Bribes Here."
Over at the Volokh Conspiracy, Eugene Volokh has an analysis of the legal issues. I had a chance recently to look at the legal issues specifically from a DC law perspective. As I read the cases, under current law, the hotel would not win a lawsuit against the projectionist (I leave aside whether the DC Council could adopt a content-neutral law regarding the projection of light communicating messages onto the buildings of others). Here is what I found