Hi Peter,
I am a little bit puzzled as to how you plan to use the moulds again. As the images of the signs you wish to make are (in the second image ) a 'one off' design so unless you can make the number part of the sign changeable then a mould is just extra work to on avail.
So unless I have missed some point, I think it needs a rethink! Perhaps you should think of just doing unique signs, after all you will be doing them just to make a mould.

Peter