The invention relates to a method of treatment of a retroreflective sheet with a treatment composition that comprises a fluorinated compound having one or more silyl groups and an auxiliary compound selected from the group consisting of (i) one or more non-fluorinated compounds of an element M selected from Si, Ti, Zr, B, Al, Ge, V, Pb and Sn and (ii) an organic compound having a Si--H group. The invention also relates to compositions comprising (i) a fluorinated compound comprising one or more silyl groups and (ii) an auxiliary compound selected from the group consisting of organic compounds having a Si--H group.