No, must and may

The high-frequency prohibitions: NO ENTRY (the solid red board with a white horizontal band — often hung in pairs on lock gates and harbour mouths); anchoring prohibited (an anchor under the diagonal — cables and pipes below, exactly like the chart’s crossed anchor); mooring prohibited; overtaking prohibited; motorised craft prohibited; and NO WASH — waves under the diagonal — which on a canal full of moored boats is the politeness law that gets enforced hardest.

The obligations read as red-bordered boards without the diagonal: the horizontal bar (stop where required — locks, customs), a number (speed limit, km/h), the horn (sound your signal — blind junctions and tunnels), the exclamation (special attention). Restrictions carry figures with bars above or below: available depth, available headroom — numbers you compare against draughtdraughtHow deep the boat reaches below the waterline — the depth she needs to float.full glossary → and air draughtair draughtThe boat’s height above the waterline — what must fit under a bridge.full glossary → before committing to the reach.

And the blue family says yes: entry permitted, a white P for berthing allowed, a white anchor for anchoring allowed, with the grey diagonal board cancelling whatever restriction came before. The exam loves mirror pairs — red anchor versus blue anchor — precisely because skim-readers confuse them; read the FAMILY first, every time.