{FAB} clan announced a merge with Forgotten Soldiers yesterday. While the former is still active with its server being rarely empty despite its high ping, the letter is practically inactive as far as I know. |FS| website is not working anymore and their GameTracker page is quiet as well. Members of the merged clans will use one of the following tags {FAB}Name|FS| or |FFABS|.
Regarding the situation in SWAT4 these days, we might see more similar fusions in the near future.