I live in SE Chester County. Lots of horse farms in the greater Unionville area. I’ve never seen a "warning’ sign. Never gave any thought to it. The vast majority of fencing around here, the majority of horse farms I have ever been on is board fencing anyway. Some, a lot may have a hot wire on the top rail.
As Clanter said, the state as William Penn outlined in his charter gives Townships (municipalities) a lot of discretion as to how they want to run things. But as more and more subdivisions have been built in/around farms. Which can and does change voter demographics/mindsets in small “farming” townships. Which bitch about farms, smell, activities, common practices. Complained that the pig farm they moved next to is hurting their property values etc and want it shut down and or demand the owners run it as a park for them. The state passed a law know as The Right to Farm. It restricts Township supervisors from enacting laws, changing zoning that infringes, restricts on and or makes it difficult, more expensive to “farm”. There have been a number of Townships that have been taken to task by the state in recent years.
As far as I am concerned. If some bone head walks on, trespasses on somebody’s farm and gets zapped so be it. Assuming the fence charger is of the standard voltage and style that has been tested and approved for the purpose and is non life threatening. Now, if someone installs a electric fence that is used in Jurassic Park to keep a T-Rex in its paddock. I would like to think that should be sign posted.
You should be able to get the answer by calling your Township. Most have all their rules and regs on their website. But have not found one that is cross indexed, has search ability. PITA to go through it page by page. Subparagraph by subparagraph.
There are lots of “laws” written that are only enforced when someone complains. I just saw/learned about a PA law that makes it illegal to mow/discharge the grass clippings on to a public roadway. The police would have a field day handing out tickets around my neck of the grass mowing woods. The state should point this out to the contractors they hire to mow.