I’d argue that the most common type of new livaboard boaters are very visible, unfortunately. His presence is known in advance (it’s usually a He), by floating debris escaping from overflowing bin bags on the back deck, and oily scum in the water. They’ll be various crap on the towpath or leaning on the hedge and quite often a convenient gap into the field behind to dump more unsavoury stuff out of sight.
The boat itself will be listing badly, with black windows either from years of filth or stick on film. It doesn’t matter, as long as you can’t see in. Stuff is piled up in the bow against the padlocked door, the hull will have last been blacked in 1987, and you’ll pity the poor bugger that did a safety cert on it.
The occupant can be an elusive breed, rarely rising in daylight during winter months, but can be identified by dreadlocks, clothing that’s all various shades of black, a coat proudly emblazoned with a company name (that he’s DEFINITELY never worked for), and of course a can of strong lager in his hand.
You’re very unlikely to ever see them on the move of course, which is a good thing. To be down wind of one for hours at 4mph isn’t going to be pleasant.