Japanese warning slogan

There is nothing wrong with your understanding of "one person and one tour", and there is nothing wrong with the requirement of accurate grammar.

However, the slogan on the lifebuoy is also the most standard Japanese expression.

....は.....です

People swim with nouns as the subject.

なぃです adjectives and auxiliary verbs together form the predicate.

See if that's what your grammar book says

In addition, slogans are generally concise, and the landlord's sentences are all aimed at "one person, one person, one person, one person, one person, one person, one person, one person, one person, one person, one person, one person, one person, one person, one person,