Green’s Dictionary of Slang

parker v.2

[Ital. parlare, to speak]

(Ling. Fr./Polari) to ask, to speak, to beg.

[UK]P.H. Emerson Signor Lippo 92: She had to parker letty every darkie and parker for somone to look arter me.
[UK]Partridge DSUE (8th edn) 855: [...] from ca. 1890.