Full Idea
Early formalism (Thomae etc) was crushed by Frege: first, mathematics must be about classes of symbols (abstract types), not the symbols themselves (the tokens); second, games may be meaningless, but meta-games are not.
Gist of Idea
Formalism fails to recognise types of symbols, and also meta-games
Source
report of Gottlob Frege (Grundlagen der Arithmetik (Foundations) [1884]) by James Robert Brown - Philosophy of Mathematics Ch.5
Book Reference
Brown,James Robert: 'Philosophy of Mathematics' [Routledge 2002], p.64
A Reaction
Brown goes on to show how Hilbert revived the formalist project. A really austere formalist view of mathematics clearly seems to be missing something basic, either in physical nature, or in the world of ideas.