Two estate agents, 1 billboard each on pedestrian barriers

Do they have planning permission to erect what are essentially advertising signs - SOLD / LET - on public property? If not, please phone them and get them to remove said signs while educating / warning them about similar activity across Glasgow.

Just like flyposting, the council seem incapable of breaking this endless cycle. Why? Because you sit back & await public reporting, then- if we are lucky - you remove the signs (at public expense). What you should be doing is phone the agents, instruct / warn them, ensuring they remove any reported signs. If their practises continue, fine them on each and every occasion. If that doesn't stop it, remove their trading licence. One phone call per estate agent to break the endless cycle Vs perpetual reporting, uplift, disposal (instead of recycle). Stop the madness please and pro-actively manage for a change. Thanks.