Is there any easy trick to know if a substance is a Brønsted–Lowry acid or base?
Not perfect, but here are a couple rules of thumb to start with for the most common cases.  The key with both rules is to look at the molecular structure.

A Bronsted acid typically has hydrogen attached to oxygen, sulfur or a halogen, all these being relatively electronegative elements.  The hydrogen could also be attached to another nonmetal, especially nitrogen or phosphorous, if the atom is a positive charge center like the nitrogen in ammonium ion.  If the atom is both a positive charge center and oxygen, sulfur or a halogen, you likely have a strong acid.

A Bronsted-Lowry base typically has a nonbonding electron pair that can combine with a proton, thus resembling a Lewis base.  In stable compounds the nonbonding pair us usually on the same kind of atom as one of the elements mentioned above for acids.  This is one reason Bronsted-Lowry acid-base reactions are typically fast and reversible.