Based on the limited information you have provided, if the parking space is part of the demised premises and rent is paid for it, then you, as the tenant, have a contractual right to use it. That right cannot be unilaterally restricted by a third party unless the tenancy agreement explicitly allows it.
If the AST contains no clause requiring a permit, then: you are not contractually obligated to display one. Any charge for failing to do so is unenforceable, especially if issued by a private operator relying solely on signage.
Landlords or managing agents often assume that signage alone creates enforceable obligations. It doesn’t—not against tenants with superior contractual rights, unless the AST includes a clause like:
“The Tenant agrees to comply with any parking regulations or signage displayed on the Property, including the display of permits as required.”
...then the signage is not binding.
If PCM is issuing Parking Charge Notices (PCNs) based on signage alone, and the you have:
• A designated space,
• No permit obligation in the AST,
• And no clause submitting to third-party terms,
...then the operator may be trespassing or acting ultra vires (beyond their authority).
As you are going to be challenging enforcement with either the landlord or the management company, you should demand the contractual basis for the permit requirement. Cite the AST definition of “The Premises” and the absence of any clause binding the tenant to third-party terms. Invoke primacy of contract... the tenancy agreement overrides signage unless the tenant agreed to be bound by it.
The only way you would be bound to comply with the third party signs is if there was a clause similar to this in your AST:
“The Tenant agrees to comply with any parking regulations or signage displayed on the Property, including the display of permits as required.”
If the AST contained wording like this, then:
• You, as the Tenant, would be contractually obligated to follow signage rules.
• A failure to display a permit could be construed as a breach of tenancy.
• A third-party parking operator could argue they’re enforcing terms you agreed to.
However, if no such clause exists, then the signage is not binding on you. Your rights are governed by the AST—not by signs erected by a third party after the fact.