George - The trollers that I see do not exhibit the dayshapes because they know they are not "engaged in fishing". Paul's boat showed no day shapes.
I do not interfere with their work when I am at play. (Usually I am working too, but there is no dayshape or lights for an vessel engaged in instruction.)
They should be a dayshape and lights for a vessel under the control of someone unaware of ColRegs, perhaps a cone with the apex up.
Excellent idea, but let's graft it onto an existing Rule for ease of IMO approval and Colregs implementation, here goes:
"New Rule 27(i):
A vessel under the control of one who is free of knowledge of the COLREGS and proud of it, including vessels not trawling but just fishing who are sorta maybe a little, but not really, restricted in ability to maneuver but wish they were, and want right of way status regardless, shall exhibit:
(i) a lava lamp ("I'm not paying attention, or am actively ignoring you");
(ii) below said lamp, two all-round red lights in a vertical line
("Captain is dead--well,okay, maybe just brain-dead");
(iii) two balls in a vertical line, with a green, yellow and purple Dunce Cap ("Happy Mardi Gras!") atop the upper ball.
And under new Rule 34(g):
A vessel subject to new Rule 27(i) shall sound, at one minute intervals, on
a whistle designed for such purpose, at least one of the following:
(i) the "Whoopee Cushion" sound;
(ii) the Homer Simpson "D'oh!" sound;
(iii) the Woody Woodpecker cackle call.
Think that might clear things up? ;-)