I know the RER name has changed, but have the signs to the stations?
Have they changed the name? Certainly I haven't seen any advice, and they haven't changed the RATP website.
Yes, they merged the RER with the "Transilien" suburban lines.
The RER retains the line numbers A to E, the Transilien lines are H, J, K, L, N, P, R, U.
Last time I went through Paris, there were still some signs with "RER", just no new ones. New signs just give line letters. AFAIK there is no new collective brand name.
The combined network map is here: https://upload.wikimedia.org/wikipedia/commons/0/0a/Transilien_Paris_region_map.jpg
well that map certainly clarifies things - like looking through mud