For mesons whose constituents are a heavy quark and its own antiquark (quarkonium) the same notation applies as for atomic states. However, uppercase letters are used.
Furthermore, the first number is (as in nuclear physics)  where  is the number of nodes in the radial wave function, while in atomic physics  is used. Hence, a 1P state in quarkonium corresponds to a 2p state in an atom or positronium.