I think that the emphasis in the question is not so much on accessibility as it is on the fact that disabled customers do not have to wait in line at the designated checkout points where they have priority over non-disabled customers. This is not quite obvious from the other two answers offered. If the sign is displayed above the checkout lane/counter there is no need to mention that word on the sign.
Priority for disabled voters. – Whenever a voter appears at a polling place and that voter has: (1) an obvious medical disability which, in the opinion of the warden, would cause the voter to experience severe discomfort by standing in line, or (2) a certificate from a licensed physician or Christian Science practitioner attesting that the voter has a disability which makes his or her standing in line inadvisable, then that voter may be allowed a priority position for complying with requirements of § 17-19-24 and in each polling place one voting booth shall be designated for priority use by these electors.
http://www.rilin.state.ri.us/Statutes/TITLE17/17-19/17-19-52...
Airlines tend to give priority to disabled travellers, allowing them to pre-board the airline first.
http://www.flying-with-disability.org/boarding_and_exiting_t...
Among the facilities on the estate are: ample parking (free at Visitor Centre, £2 at Studley Lakeside; priority for disabled visitors at West Gate); baby feeding/changing areas; restaurants and shops.
http://www.fountainsabbey.org.uk/visiting/facilities5g.html
Medical Priority for Disabled Veterans
Veterans Affairs officials want to send veterans with service-connected medical problems to the front of the line when it comes to receiving medical treatment at VA facilities.
http://www.vnis.com/story.cfm?textnewsid=761

Riječ "handicap" rjeđe se koristi u Americi od riječi "disabled" jer se više ne smatra politički ispravno. Osoba sa shizofrenijom može biti djelomice onesposobljena iako nema vidljvi odnosno lako uočljivi hendikep. "Disabled" je možda širi termin za potencijalni invaliditet.



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Note added at 22 hrs (2006-10-10 06:53:59 GMT)
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It goes without saying that if something is handicap accessible, priority is given to those primarily with physical limitations, such as a person in a wheelchair. There are plainly visible and "invisible" disabilities. It may be a matter of subtle differences in language used in different countries. I believe disability encompasses all limitations. Also, though a person in the U.S. may be disabled and continue to drive a car, he cannot legally park in a handicap parking space without a special sticker on his license plate.