Real World article
(written from a Production point of view)

According to the script for the Star Trek: The Next Generation episode "Yesterday's Enterprise", Station Salem Four was a location that was raided by the Bel-Zon. It is unknown if it was related to the canon Station Salem-One.

In an alternate reality, where the Federation was at war with the Klingon Empire, Captain Jean-Luc Picard and Guinan debated the merits of returning the USS Enterprise-C to its time period. If the Enterprise was returned, Guinan believed that history would readjust itself. When arguing against readjusting history in an effort to prevent lives that might be lost in a war, Picard gave this example as one where preventing an action from happening would prevent a war and the subsequent loss of life. The line in which Station Salem Four was mentioned did not make it into the final episode.