These two jerks at Ft. Tilden this didn't seem to care that, in addition to being inconsiderate, they were breaking federal law, with some nasty consequences to them if it were ever enforced.
There are also plenty of signs. Here are just two of them:
The rules about pets in national parks are contained in 36 CFR and you can read them for yourself here. We've just put up a link in our sidebar. Following are relevant excerpts:
§ 2.15 Pets.
(a) The following are prohibited:
* * *
(2) Failing to crate, cage, restrain on a leash which shall not exceed six feet in length, or otherwise physically confine a pet at all times.
* * *
(c) Pets or feral animals that are running-at-large and observed by an authorized person in the act of killing, injuring or molesting humans, livestock, or wildlife may be destroyed if necessary for public safety or protection of wildlife, livestock, or other park resources.
(d) Pets running-at-large may be impounded, and the owner may be charged reasonable fees for kennel or boarding costs, feed, veterinarian fees, transportation costs, and disposal. An impounded pet may be put up for adoption or otherwise disposed of after being held for 72 hours from the time the owner was notified of capture or 72 hours from the time of capture if the owner is unknown.