Early 19th century; earliest use found in Leigh Hunt (1784–1859), poet, journalist, and literary critic. Partly from placard + -er, and partly from placard + -er. Compare French placardeur.
Definition of placarder in US English:
placarder
nounˈplakɑːdə
A person who puts up or carries placards.
Origin
Early 19th century; earliest use found in Leigh Hunt (1784–1859), poet, journalist, and literary critic. Partly from placard + -er, and partly from placard + -er. Compare French placardeur.