In the first place, although ‘franking’ is a legitimate English word, its meaning is different from that of ‘frowning’, which is what is expected in the context of ‘face’. As an adjective, to be frank is to be honest or blunt in speech or writing. As a verb, ‘frank’ means to print a mark on a stamp so that the stamp cannot be used again; or to print a mark on an envelope to show that the cost of sending it has been paid.
Secondly, ‘frown’, the word the speaker should use instead of ‘franking face’, does not require ‘face’ because the latter is naturally embedded in its meaning. In other words, ‘frown your face’ is also wrong as it is tautological. You only frown, you don’t frown your face.Using ‘frown’ also demands caution. This particularly has to do with the preposition to use with it. Especially as a verb, it collocates with ‘at’ and ‘upon’.