From  My Garden, ‘an intimate magazine for garden lovers’, no. 129, September 1944:

‘How many people know that sloe [Prunus spinosa fruit] juice may be used as an ink for marking linen?  Plunge a clean nib into a ripe sloe; the writing will not wash out, and no application of heat is necessary.’

Image:  Tooting Common, London Borough of Wandsworth, November 2022.