Yeah, that was me. Kosmo's official announcement says LFG/LFM (which is now entitled 'Grouping'). Even Sparker's note says Social then specifies LFM. And I have not personally heard or seen any complaints from people banned or warned for posting info in the 'Who' comments. Maybe this method is not being used, or maybe they are not being reported.
If there was a general in-game ban on advertising trades, they would have and should have stated that in the official announcement. They didn't; they specified LFG/LFM. 'Who' comments are innocuous and non-invasive. They require the poster to uncheck anonymous to be read and require other players to scan through the Who list to find you. Additionally, they reset with logout requiring the poster to update as information changes.