Subspace signature
A subspace signature was given off by various objects that utilized subspace which allowed those objects to be detected by scanning for each object's unique imprint.

Starships
Each starship had its own unique subspace signature which was logged by Starfleet and could be determined by all Starfleet vessels.

In 2152, the  detected the subspace signature of a temporal timeship from the 31st century. ()
Lieutenant Commander Data, in 2368 on stardate 45571.2, detected the subspace signature of the  near an unexplored moon of Mab-Bu VI. ()
's nacelles gave off a very similar subspace signature to a large space-dwelling lifeform which threatened to rob the ship of its power. ()

Transporters
Subspace transporters could also leave a "trail" of particles after they had been used.

Data and Geordi La Forge, in 2370 on stardate 47829.1, scanned Captain Picard's ready room to find a subspace signature on a chair which Bok had sat in beforehand that was determined to have originated from subspace particles produced by Bok's personal subspace transporter. ()

de:Subraumsignatur
signature
Identification technology