There's a fantastic, swift guide to your first amendment rights, and it's of particular interest to photographers - amateur or otherwise. But the guidelines apply for general, free speech rights as well. It's available here, courtesy of the ACLU.
In the wake of recent events in Baltimore, Ferguson, and as a simple youtube search for "philly police brutality" will show, police officers routinely - and illegally - seize or destroy video cameras of bystanders who are not involved in any criminal activity. We'd list links to the videos here, but there's simply too many, unfortunately.
You should always exercise your free speech rights, and never be cowed from so doing: but remember - in the face of a highly antagonized law enforcement culture - this simple practical tip:
Don't piss them off.
Police departments don't exactly hire constitutional law scholars (and, unfortunately, have been publicly exposed for refusing to hire the best and the brightest), and to some extent, you can't blame them. They have a horribly difficult and dangerous physical job to do. Wimpy lawyers can't (and probably shouldn't) do the job.
But too often, the cops in Philadelphia have famously short fuses. So speak your mind, but do not, under any circumstances, actively antagonize law enforcement. You may have a right to videotape an arrest, or photograph the Ben Franklin Bridge or Independence Hall or what have you, but if you mouth off to a police officer in the process of so doing, they will absolutely ruin your weekend by forcing you to spend it in the Roundhouse at 8th and Race.
It pays to be polite, even when the boys in blue are in the wrong. In that event, document everything, and immediately contact the Law Office of J. Conor Corcoran, P.C. at 215-735-1135, should the Philadelphia Police take a bite out of your Apple.