You can fight it. Parking tickets can be won.

I'd say that you work from home and haven't used your car in a week or whatever so you never noticed the newly added signs. Don't ask to have the ticket wiped out. Admit that it was your fault for not checking, but 150 will really hurt your tight budget. Ask if the fine can possibly be reduced. I find that admitting fault and asking only for a reduction a lot of times they just wipe it all because the judge thinks you are taking responsibility. If you go on a rant blah blah blah then the judge is mostly fuck this loud mouth and makes you pay the full amount.

Edit: saw you ask about in person or online. I'd say in person is the better chance to win. Judge sees you took the time to come and ask for the reduction. You're more invested than the 5 minutes to contest online.

Stay calm and a nice tone. Raising your voice or turning your questions or requests into a rant will almost always get you nothing in the way of leniency.