Man pages matching name sd_bus_signal in section 3:

SD_BUS_SIGNAL.3.en	debian 11 / libelogind-dev-doc
SD_BUS_SIGNAL.3.en	debian 11 / libsystemd-dev
SD_BUS_SIGNAL.3.en	debian 12 / libelogind-dev-doc
SD_BUS_SIGNAL.3.en	debian 12 / libsystemd-dev