I haven’t used Signal.
Is your ‘registered Signal number’ your phone handset number?
From this page:
https://support.signal.org/hc/en-us/articles/360007318691-Register-a-phone-number
[You are right, Delta Chat uses AutoCrypt, which is OpenPGP based.]
Winamp Skins Collection link
( * Has some NSFW skins mixed in.)