The sign, which reads "Please this is not a public toilet", was put up a few weeks ago outside the shop which was formerly Jones Bootmaker and Elts.
But staff and campaigners think the lack of free public facilities open at night are forcing people sleeping rough to use the area as a toilet.
Manager Brian McGaw said the issue had stopped since the signs had been in place but they were ripped down earlier this week.View this post on Instagram
A post shared by @femaletoiletreviews
He said: "We have had a homeless person sleeping in our doorway who was using our entrance as a toilet.
"It hasn't happened for a couple of weeks since we have put the sign up and it seems to have stopped.
"When Caffe Nero is open they will pop in there but at night they will use our doorway as there is nowhere else to go."
Staff have had to clean the area down every morning using bleach and water to get rid of the strong smell of urine.
"The smell of urine would hang around all day, it was really strong.
"It is also degrading for staff as they were having to go out every day and try to clean it with bleach."
Public toilets in Worcester
There are public toilets in the Cornmarket and Angel Place, however, these cost 20p.
Free toilets are available at The Guildhall and Crowngate Shopping Centre but are closed at night.
Instagram page Female Toilet Reviews posted pictures of the signs outside the shop.
She posted: "Maybe if there were more free public toilets around the city, or temporary urinals for men AND women on a night out people wouldn't feel the need to wee on The Shambles.
"If anyone has seen this toilet being used in the day, please let me know."
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The reviewer, who like to remain anonymous, reviews public and customers toilets in Worcester in an effort to improve the standards.