I'm no philatelist and I wouldn't think of dispensing philatelic advice. But I'm guessing that CFS Bermuda is the only HF-DF station featured on a postage stamp, given that information about such places used to be more typically mailed on microdots.
Issued by the Bermudian government in 1996 as part of a set commemorating former Second World War and post-war bases in Bermuda, the CFS Bermuda stamp shows the Canadian Forces symbol, some generic looking antenna masts, and Canadian personnel at work in the operations room. The actual HF-DF array is not depicted.
(Belated kudos to DND's Defence Matters
, vol. 2, no. 3, April 1997 for mentioning the release of the stamp.)
NRS/CFS Bermuda operated from 1963 until 1993, providing cut-off bearings on Soviet missile submarine transmissions and other maritime targets.
Interestingly, the Bermuda HF-DF station was not the only Cold War-era naval SIGINT system immortalized by its own postage stamp. The U.S. Navy's WHITE CLOUD ocean surveillance satellite system, first launched in 1976, was actually shown in some detail on a U.S. stamp issued that year.
[Update 28 June 2015
As can be seen here, the satellite was actually depicted on something called a "space cover
", an unofficial, commercial product created for collectors, rather than a government-issued stamp. The artwork and other information on such items was often far from accurate, but in this case it was apparently pretty close.
An almost identical image was later printed in Aviation Week and Space Technology
("Navy Ocean Surveillance Satellite Depicted
," Aviation Week and Space Technology
, 24 May 1976, p. 22). According to space historian Dwayne Day, that image "is consistent with a series of [subsequently] declassified drawings dating from 1973 and depicting the Multiple Satellite Dispenser and outlines of the sub-satellites" (Dwayne A. Day, "Above the clouds: the White Cloud ocean surveillance satellites
," Space Review
, 13 April 2009).
Update 29 June 2015
Based on his own research into the question, Dwayne Day concludes that the Aviation Week
article came first and that the space cover, although apparently postmarked on the day of the launch, was printed later.]
Are there any other SIGINT stamps out there?