A Hanging Banner for the Front of the Booth
There is a plethora of materials and techniques. For example there are a variety of close weave canvasses used by artists for oil painting. These can be bought by the yard (or meter). They need priming first. They will take artists oil paints or acrylic paints, both of which are flexible, waterproof and durable. Do not use varnish. Proper varnish doesn't dry out completely for around 6 months. But anyway any kind of gloss reduces visibility - that's why puppets should never have a glossy finish. You could use a matt or eggshell varnish.
The most important thing to consider is the permanence of the colours. Many colours which are based on dyes (as opposed to pigments) fade very rapidly in daylight.
Prof. Mark Poulton who is a skilful sign-writer says: I use 'Calico', painted over with diluted white emulsion. Then I paint the over the top with acrylics.
No varnish required.