What I mean is, although illegal, the council's enforcement office has neither the money nor the staff to patrol the town six days a week to check for illegally parked or fly-posting. So, they rely on people complaining.
It's like the A-boards and other advertising outside shops, depending on the width of the pavement, the shop should get permission from the council before placing them outside, in case it causes an obstruction (especially to those with prams, pushchairs or wheelchairs), but how many actually do?
Thing is, it actually is different if the advert is on a bike. The op suggested locking the bike to a lamp post, which clearly could result in a fine if it were any bike. Lamp posts have access hatches for a reason..
But thinking more broadly, there are provisions in all modern town centres for parking up bikes. And all of such central spaces also have strict rules about signage and advert hoardings.
But... If bikes are allowed in a space, then there is nothing that can be done if that bike carries an advert. There is not one single law the prohibits advertising on bikes or in fact any other mode of transport.
Obviously you're likely to upset local competitors so you need to be damn sure the bike is legally parked up. But if it is, there is nothing anyone can do.
Even the government is behind this idea. The 'Boris bikes' in london all carry Barclay bank decals. And Raleigh have been rudely advertising themselves on bikes for years
My point is this is established and allowable, but really under-utilised. If you have a business within 50m of a legal place to lock up a bike, go get an old bike from free ads and slap an ad on it. In fact go nuts, spray it pink and glittery. Strap a plastic penguin to the handlebars one day, and a giant inflatable squid the next. Clip 30 padlocks to the spokes and see if you can get others to start doing the same. Make it a thing that attracts attention by being different.
I absolutely love the idea and think the potential is very exciting. It's fascinating to think that in the modern world with so much red tape, you can legally secure a 6' long patch of town centre real estate free of charge, and decorate it as you wish (unlike the adjacent buildings no doubt) so long as underneath your art and ads there is a bike.
People often ask what separates a business owner from an entrepanuer. Choosing to place a 'look at me' bike in a busy spot is a better qualification of being an entrepanuer than most others I've heard.