pamac allow installation of a package from a repo without a .sig file.
I am using a full mirror of Manjaro mirror, and in that mirror I deleted a .sig file for a package (example calc-2.13.0.1-2-x86_64.pkg.tar.zst.sig) and with the default pacman.conf I can't install that package (give error of missing .sig file), but pamac will install the package without giving any complain whatsoever. I tested it from pamac cli with the following versions libpamac 11.1.0-1 and pamac-cli 10.2.0-1.