Hi Shari,
'On ne peut pas stationner ici' is 'You cannot park here'...
The you here applies to everyone, in other words, it is forbidden to park here.
It is a bit like:
On ne sait jamais ce que nous réserve l'avenir = You never know what the future holds
Which is a saying for a truth that applies to everyone.
Not sure what you mean about the verb tense not matching...