Visible panty line, or VPL as it is usually shorthanded, is a fashion faux pas to be avoided. That is especially the case, it seems, if you're already a serving member of the thin blue line.
A dictat issued to West Midlands police force has cautioned officers that their underwear is required to be "an appropriate colour" and "inconspicuous" beneath their uniform.
Thongs or boxer shorts creeping over waistbands, or colourful bras peeping through regulation white shirts, are outlawed under the sartorial guidance, issued as part of a revised uniform policy.
The warning is apparently needed to ensure officers present a "professional and corporate appearance" to the public.
But recipients are less than happy, accusing their superiors of "nannying" and criticising the warning as "outrageous".
In a lively response in the pages of Police Review, officers question the force's entitlement to dictate their underwear, or the need for such a directive, with some asking if there would be "spot checks".
"Any chance they could run a piece on tying shoelaces, or how to use toilet paper?" inquired one constable.
Another chimed: "Rather than spending time on sending pointless messages out concerning the way we look when doing the job, the force should concentrate more on letting us do the job of a police officer trying to catch criminals." A third stressed: "We are not a scouting organisation made up of young children who need nannying."
Assistant chief constable Sharon Rowe, defended the policy saying: "All supervisors, at whatever level they are in the organisation, have a clear mandate to challenge inappropriate dress."