Officers from Market Drayton shared the photograph on Tuesday, showing a small lock knife that had been taken into a town school by a pupil.
The knife, 10cm long, has a serrated 4cm locking blade.
A spokesperson for the town Safer Neighbourhood Team said: "The knife has a blade that locks into place and as such, is illegal to have in a public place and/or a school, contrary to sections 139 and 139a of the Criminal Justice Act 1988."
The police are asking anyone who knows someone carrying a knife to look at the force's Steer Clear programme, a targeted education and engagement programme aimed at young people who are believed to be, or may become, involved in knife related crime.
The discovery comes at a time where forces up and down the country are running Operation Sceptre, a week-long national campaign aimed at tackling knife crime.
West Mercia Police Superintendent Edward Hancox said: “We know the devastating impact knife crime can have on not just the victim but their families and the wider community.
"It can also be life-changing for anyone who is caught carrying a knife, we know those who carry knives are just as likely to be a victim of knife crime."