A method for marking a petroleum hydrocarbon, biodiesel fuel or ethanol fuel by adding to the petroleum hydrocarbon, biodiesel fuel or ethanol fuel at least one compound having formula (I) wherein R1 and R2 independently represent at least one substituent selected from the group consisting of hydrogen, C1-C12 alkyl, C1-C12 alkoxy and nitro; and R3 and R4 independently represent hydrogen, methyl or ethyl.