"An Essex Police spokeswoman told Sky News: "We are trying to identify the officer from the video footage to establish the circumstances around what happened.
"In the meantime, we would encourage the driver to get in touch with us."
However, Essex Police has not commented on whether it considers displaying a "B******* to Brexit" sign to be a public order offence.
Nottingham Magistrates' Court reportedly ruled in 1977 that "b*******" was not an obscene word in the case of a record store manager who had been arrested for displaying the Sex Pistols' debut album Never Mind The B*******, Here's The Sex Pistols.
Earlier this year, the Liberal Democrats MEPs wore t-shirts including the phrase "B******* to Brexit" in the European parliament."