I found an interesting question on Math SE asked by @KCd, but it is over four years old without a clear answer. Since it seems to be more on topic here than on Math SE, I thought to post it here in case it receives good answers.
(I commented on the post a few months ago asking the OP if they would be interested in posting the question here, but since I did not receive any reply I'm making my own post; I hope there is no objection to this, but if so please let me know.)
This question is being asked on behalf of a graduate student in my department. When and where did the tradition start of a seminar or colloquium speaker using just the first initial of the speaker's last name (or initials for the speaker's first and last names) when stating a theorem due to the speaker? Attributions of results due to anyone else, including joint theorems with the speaker, are usually indicated with the other people's full last name.
Anything like a photograph of Hilbert giving a talk with "Satz (H.)" at the start of a theorem would be great to see if it exists.