So I had 'OSS' on my boarding pass for my connection in YHZ the other day coming in from :LHR and connecting to YYT. YHZ has constructing ongoing in the screening area so that the line up to get into security stretched well out into the atrium. As my connecting flight to YYT was delayed by a few hours due to weather, I got a coffee and waited til things had died down a bit. Before I could present my BP to the agent at the end of the line, I was called over for enhanced security screening (swabbing bag, laptop etc) the payoff of which was being sent into the priority line and getting through security in 5 minutes as opposed to 30+. So I got lucky and OSS, in YHZ at least, appears to be a waste of time.