The cable car railways in San Francisco are tagged as [railway=tram][1] (with [oneway=yes][2]) ([example][3]). The corresponding [route relations][4] use *railway=tram* and *tram=cable_car* ([example][5]) although there are [not many][6] relations with the cable car tag.
tag. And of course you can also map tram stops with the [railway=tram_stop][7] tag ([example][8]).
[1]: http://wiki.openstreetmap.org/wiki/Tag:railway%3Dtram
[2]: http://wiki.openstreetmap.org/wiki/Key:oneway
[3]: http://www.openstreetmap.org/browse/way/144344606
[4]: http://wiki.openstreetmap.org/wiki/Relation:route
[5]: http://www.openstreetmap.org/browse/relation/1959009
[6]: http://taginfo.openstreetmap.org/tags/tram=cable_carhttp://taginfo.openstreetmap.org/tags/tram=cable_car
[7]: http://wiki.openstreetmap.org/wiki/Tag:railway%3Dtram_stop
[8]: http://www.openstreetmap.org/browse/node/317081446