Yes I remember that, a few others had similar notices too.
Reading Borough Council has had signs at various locations for many years that demanded a charge for mooring. They even employed someone to collect the payments for a while but he didn't have much success which is what led to RBC using DE. As riparian owners, RBC have the right to charge for ''landing'' and/or for use of facilities ( my own interpretation ) such as landing stages, wharves, mooring rings or bollards. BUT, what is unclear is do they have a right to charge for the first 24 hours and can they forbid mooring at certain locations? The stretch upstream of Caversham Bridge used to have no restrictions but now mooring is forbidden for about a mile. The PRN includes anchoring or mooring for ''a reasonable time'' without charge, The Thames Conservancy Act interprets this as 24 hours but if circumstances ( such as strong stream, or breakdown etc ) require longer then the master of a vessel should be within his rights not to pay.
Let me say that I have no legal experience, this is just my opinion from what I've read.
Keith