Both Uses

petty
in
Flags of Our Fathers
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He studied it for a minute, then thrust it under the gaze of Navy Petty Officer Felix de Weldon.†
Chpt 12. *
The local newspapers highlighted the arrests until they grew so commonplace they were no longer a novelty; then they dropped Ira's scrapes with the law into the police log, with the rest of the petty-crime news.†
Chpt 18. *

Definitions:

(1) (petty as in: a petty crime)
of less importance -- at times implying insignificance
(2) (petty as in: don't be petty)
unpleasantly focusing on an unimportant flaw; or attempting to make someone suffer for an unimportant wrong
(3) (petty as in: petty officer)
a non-commissioned officer

Petty officer typically refers to a Navy or Coast Guard officer who is subordinate to commissioned officers and chief petty officers.
(4) (meaning too rare to warrant focus)