Lying under oath

Spotted this sign at the gas station today. Trying to work out why truck drivers would lie under oath while parking.

perjury (ˈpəːdʒ(ə)ri/) noun
1. the offence of wilfully telling an untruth or making a misrepresentation under oath. "he claimed two witnesses at his trial had committed perjury" synonyms: lying under oath, violation of an oath, giving false evidence/testimony, bearing false witness/testimony, forswearing oneself, making false statements, wilful falsehood