yarn bomber
noun /ˈjɑːn bɒmə(r)/
/ˈjɑːrn bɑːmər/
(also yarn stormer
/ˈjɑːn stɔːmə(r)/
/ˈjɑːrn stɔːrmər/
)- a person who decorates items in the streets with colourful pieces of knitting or other items made using wool, cotton, etc., often doing it secretly