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No it is not legal. It is defacement of property.
Some words that rhyme with "understatement" are abatement, defacement, and merriment.
cachet
Most collectors would consider it a defacement and reduction in value.
Marking property without the owners consent is considered defacement and vandalism and this is a punishable crime
Phillip Foss has written:
'Somata'
'Yana'
'Chromatic defacement'
'Roaring Fork passage'