Well, that didn't take long!
Thank you for contacting Geocaching HQ.
Where in the world is Signal? Dönerstag 2017 has been granted to HoustonControl!
Geocaching Community Manager
Did anyone else not get the souvenir for attending a Donerstag event? I went to the Donerstag and CITO at night on the UHCL Trails (https://coord.info/GC72XDR) and logged it from the Geocaching app, immediately getting a pop-up box that said "Congrats on receiving the Donerstag Souvenir!" (or something to that effect), but I still don't show the souvenir in my profile. I have a help ticket in to GCdotcom, so we'll see what happens.