Complain to the Olympic board as McDonalds are a sponsor of the Olympics and the Para-Olympics.
In parallel write/email to the newspapers etc.
Also talk to your embassy who can advise how to proceed in other ways.
You have a vision problem and need a visual aid to combat that disability. McDonalds not only commited assualt but also did it systematicaly and premeditated way indicating they are not a suitable sponsor for the para-Olympics.
If they won't deal with this issue responsibly, then sod em and shame them as publicly and in as many ways as possible; you have done nothing wrong, nothing and they are all to blame so shame them.
Also few links on FB and twitter with liberal abuse of #mcdonalds #imlovinit #mcd and the like will soon garner this issue the attention it needs and deserves.
You could see a lawyer, but it's hard to find one who can deal with this. I'd go the press/PR route (then a good lawyer will come to you) as your doing but with a few nationals who will happily run this story. Now is a good time given there large marketing event called the Olympics, leverage this time and educate McDonalds.
Last time I went to McDonalds security told me the toilets were for customers only too which I pointed out that in a civilised World we wash our hands before we handle our food and I had no desire to take my food into the toilet or leave it unattended as I had no confidence on the security being able to saftly protect my food/possesions. He appologised and I left to eat elsewere.