よくし (抑止)

I've learned a lot of new words lately been lazy about uploading them. This one I learned from context right now so I thought I'd share. I don't think it's so conversational, most likely train jargon... but the line was stopped and some girl I didn't know, holding hands with her boyfriend, read the sign out loud (so I didn't even have to look it up!) and asked her boyfriend what it meant and he said, approximately: duh, this. Of course this is a "check" of the lines to make sure they are clear after a suicide jump. According to my dictionary (but haven't checked with a native speaker yet though) it can also mean 'checkmate' which is pretty cool. This is like the third jump in less weeks. This season's been pretty rough.