The sign, if an external one, may have been made from exterior grade mdf
1220x2440x18mm Exterior Grade MDF
Medite Exterior is an MDF panel developed specifically for use in a wide ra
nge of external applications in accordance with MDF-H2 as defined in EN 622
part 5 and gives all the design freedom of Standard MDF. Used as a substit
ute for softwood, hardwood, plywood, plastic and metal in non-stressed appl
ications. It can be used for a wide range of external applications includin
g: External signs, shop fronts and external woodwork including fascias, ext
erior mouldings, door parts - raised and fielded panels, garden furniture c
omponents, exterior display
stands, marine craft interiors and sports score boards.
Never tried it myself though I have seen various pieces in Garden centres d
esigned for external use using it.
What I have seen has had a slight green tinge to it in its narural stste.