Regarding the preferred parking, the credit requrements state "Clearly identify and enforce for sole use by green vehicles." (emphasis added). Are there any specific enforcement requirements that need to be met?

The credit form (v1) doesn't include this part of the requirement, although they do change over time. There's also nothing more about this in the reference guide - except maybe the example signage diagram for the spaces which now adds "Permit Required" below "Green Vehicles Only". Is that the requrement - that the owner develop a permitting system to enforce "Green Vehicle" parking?