Photo special: this week special large beer

I spotted this sign outside a cafe in Funchal, Madeira last year. Down by the harbour, as I recall.



(If you can't see the photo, the sign reads: "THIS WEEK SPECIAL LARGE BEER".)

It makes me wonder. Is the large beer special because it is being offered at a special low price, or because it is something that the cafe doesn't normally offer? Or perhaps there's another explanation entirely - suggestions welcome.