The sculpture was left on a footpath sign just off the bridge over the South Forty Foot Drain on Grantham Road.
Disturbingly, it was left opposite a school.
A local resident shared the image of the sculpture with the Standard before it was removed by police.
The mystery erection comes just days after four new traditional ‘welcome to Boston’ signs were installed across the town.
Inspector Fran Harrod from Lincolnshire Police said: “We were called to reports of a mannequin torso which had been defaced and left with an accompanying sign in a very public space in Grantham Road, Boston, near to a busy shopping area. “This was deliberately provocative, designed to catch people off guard.
“The person reporting it was very distressed at the sight, as we expect many others would have been.
“The fact that this mannequin depicts a woman on the receiving end of horrific violence, and that this is displayed opposite a school, is especially distasteful.
“It is believed to have been placed on Grantham Road between 4pm on 11 January and 8am on 12 January.”
She added: “We are treating this a public order offence, and would appeal for anyone with dashcam footage or CCTV of the area around the time of the incident, to come forward.”
One anonymous reader who saw the sculpture said: “It is obviously making a statement about the number of stabbings we’ve had in this town in the last few years.
“It’s not a great welcome to Boston, but I guess that is the point.”
Another said: “Looking at it I would say some would find amusing and others would find it very perturbing.”
Back in 2016, Home Office figures revealed that Boston was the ‘most murderous place’ in England and Wales due to its murder rate - which is calculated by the number of murders and attempted murders there are, factoring in population size.
Anyone with information about this is asked to contact police by dialling 101 and quoting incident 40 of January 12.
Alternatively you can call Crimestoppers anonymously on 0800 555 111.