I'm not a boat owner but am frequently on the water skippering the local Canal Trust trip boat. In my opinion, every boat should have to display a valid licence, just like on a road vehicle (do agricultural vehicles have to display one? I don't know). Even if your 'terms of employment' are such that you get a licence as part of your job, there's no reason why you should not have to display a valid licence. There should be nothing on the licence which may stigmatise anyone, so if it's being paid by the DSS or whomever, that needn't be shown. BW boats should have to display a valid licence as well for exactly the same reason.
I've seen only this week, hung from a local roadside lamppost, a number to ring if I see an un-taxed car. There's no reason why BW couldn't do something similar (if they don't already, maybe not from a lamp post...). My view is that every licence fee collected is a few more bricks in a lock wall repair, and as system users, that's something that is in all our interests. I fully understand that some people just like to keep their heads down and get on with life. No-one says you have to report unlicensed boats, but if there's a suitable, easy-to-use framework in place, for those that are happy with reporting these ne'er do wells, they can continue to do so as far as I'm concerned. I'm now back to lurk mode.
