It is interesting that though the more X and most X constructions have been slowly replacing the older Xer and Xest in the comparative and the superlative forms of nouns adjective, they are not in free variation. Something to do with syllable count.

faster
?more fast
heavier
more heavy
curiouser
more curious
*polysyllabicker
more polysyllabic

Ceci n'est pas un seing.