I (ab)use it for my packages
Not the raw fingerprint itself, but its base64url-encoded form as a component of the package hash:
sdl-0.5.0+3.4.8-​SDL--​k4DpgH323IfF6cEaGzKUdtUQv1azbBmmcv0RMAu.tar.gz
sdl_linux_deps-0.0.0-​SDL_l​tg8hgAOayMwFN6BhHW3Rs5UPtf6n8m-2qcQHuGS.tar.gz
zigglgen-0.5.0-​ziggl​tzDLwA0Gk0Pj6QMij1j6Z_jkvGEtGKBM6-YlI_s.tar.gz
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