Phthalocyanines and their use as markers

The invention relates to phthalocyanine of formula (I), wherein Me means twice hydrogen, twice lithium, magnesium, zinc, copper, nickel, VO, TiO, AlCl, AlOH, AlOCOCH3, AlOCOCF3, SiCl2 or Si(OH)2, at least four of the radicals R to R independently mean a five or six-membered saturated nitrogenous heterocyclic radical which is bonded to the phthalocyanine sceleton by a cyclic nitrogen atom and may contain other heteroatoms, and optionally, the remaining radicals R to R mean hydrogen, halogen, hydroxy sulfonyl or C1-C4 dialkyl sulfamoyl, with the exception of tetrakispiperidinyl phthalocyanine. The invention also relates to the use of phthalocyanines substituted by heterocyclic radicals for marking liquids such as mineral oils which contain phthalocyanines of this type.