A touchscreen detects where its surface is touched. Two technologies matter in signage: projected capacitive, which senses the electrical field of a finger, and infrared, which detects a beam being broken just above the glass.
The difference decides the deployment. Capacitive is accurate, supports multi-touch and resists scratching, but needs skin or a compatible glove and gets expensive at large sizes. Infrared works with anything solid (gloves, a pen, a knuckle) and scales cheaply to very large panels, but sits in a raised bezel that collects dust and can be triggered by an insect or strong sunlight.
The caveat is that a public touchscreen lives a harder life than any specification anticipates. It is operated with wet hands, through gloves in winter, by people pressing far harder than necessary, and cleaned with whatever is available, including solvents that destroy anti-glare coatings.
Specify for the environment rather than the demo: gloved use outdoors or in cold storage rules out capacitive, food service rules out an infrared bezel that traps grease, and anywhere public needs a coating rated for repeated disinfectant.