The cynic in me says the signs are confusing because it increases revenue.
But then I may be ascribing to malice that which is the result of incremental institutional incompetence.
Some of the complaints here are classic "lazy programmer" reaction to unavoidable complexity--make the solution easier by solving a different problem. Sometime's that's the right approach, but someone isn't incompetent for choosing a more complex solution that solves a problem more precisely.
But no citizen can actually protest a parking ticket on the grounds of bad signage.
Well consider Ferguson, the city with such out of control fines/fees that there are more warrants for the arrest of citizens who owe fees for minor infractions than there are citizens!
Historically governments have had such asymmetric power over individuals that we take for granted that signs are beyond reproach. What is so inspiring about this designer's work is that it is so refreshingly democratic.
A lot of municipalities are also being screwed pretty hard by state-level policies. Many states cap how much a municipality can raise through "legitimate" taxation (eg, property, sales and income taxes) while imposing mandates on what services the municipalities must provide. Meanwhile, municipalities have an even worse time taking on debt than the state government. So it's not too uncommon for a municipality to end up in the position of being unable to meet its obligations, having nothing left to cut, and no authority to raise taxes.
My wife successfully contested an expired meter citation from Fort Worth just a few months ago for that very reason.
Personally I would doubt that the signage was made purposefully confusing out of "malice". But any attempt to simplify it, now that it exists, will have to deal with a "but it will decrease revenue" excuse.