When I visited the recently opened Starbucks near Horniman Circle, I noticed this on the glass door:
The fact that the word free has two senses in English is often brought up because the difference in the two senses is sometimes critical/relevant. Especially in the FOSS (Free and Open Software) world, the distinction is often explained as Free as in free speech, not as in free beer, to disambiguate the two senses: one of freedom and another of not having to pay anything.
I am reminded of a conversation I had with my Japanese friends last year in Tsukuba. One of the girls had recently broken up with her boyfriend whose name meant _Sugar_ in Japanese. I saw a food packet with the text Sugar-free on it and showed it to her as a joke on her current state, and recall her being a bit confused about this use of the word free. Other related languages usually have two different words for these two senses. In French, you say libre for the free speech sense, and gratuit for the free beer sense. EtymOnline claims that the sense of _given without cost_ comes from the notion of free of cost, which invokes the original freedom sense.
I found it mildly interesting that flipping the order in the phrase X free switches the sense of free being used. When we say free X, we are using the no-money sense, while X-free implies that we are free of X, where we use the freedom sense. Both forms have different syntactical structures. If you say Free WiFi, the whole thing is a Noun Phrase with WiFi as the head and Free as the modifier. On the other hand, a term like Sugar Free is not an NP. It’s an Adjectival Phrase with Sugar as the modifier and Free as the head.
In this particular case, we have the second format being used, but with the first sense. The reader is expected to either read it as WiFi (is) Free or WiFi: _Free_ or probably just see the words WiFi and Free and put 2 and 2 together.