Glue the lid shut or solder it shut and with a bold marker pen write SHARPS on the lid of the tin. Alternatively get yourself a sharps box and when full take to your local doctors who will dispose of it for you.I've been collecting mine in a tin under the sink, but what to do when its full?
Where I live, we only have one recycle bin, it's for glass, paper, metal and plastic. I assume it's taken away and sorted.
A few months ago I was watching a local news item and they were showing this inside of a recycle plant and it showed a conveyor belt moving all the recycle material, with pickers standing each side of the belt, plucking out the different materials into different bins.
I would hate the thought of my tin of used razor blades being handled by these people!..