Anti-climb paint

A sign on a fence in Greenwich, England, advising of the use of anti-climb paint.
Anti-climb paint on a gate in the UK

Anti-climb paint (also known as non-drying paint, anti-intruder paint, anti-vandal grease) is a class of paint consisting of a thick oily coating that is applied with a stiff brush, trowel or by hand using a protective glove. In appearance it is similar to smooth gloss paint when applied but it remains slippery for a minimum of three years thereby hindering an intruder from gaining a foothold.