Earth developed warp engines in 2063. The Romulans and Klingons didn't know that Earth existed until the 2150s.
But a Pre-Warp earth would have most likely gone unnoticed, since it was the fact that Human's had Broken the Warp Barrier than lead a Passing Vulcan Scout ship to make first contact.
Pre-warp Earth did not go unnoticed. Vulcans were there as early as the late 1950s, seen in the Star Trek: Enterprise episode "Carbon Creek" ProfessorTrek 02:29, July 18, 2011 (UTC)
Perhaps there was something like the Protected Planets Treaty in Stargate SG-1 but that's not canon
The Romulans and Klingons didn't know about Earth (or humans) before humans developed a warp drive.