How should wheelchair accessible facilities be denoted?

I have the opportunity to have a hand in updating a list of meetings for a fellowship I belong to. Some of our facilities are not wheelchair accessible. On the schedule, I believe the default should be that they are not wheelchair accessible, and the ones that are wheelchair accessible should be denoted with a "W." Their is a group of people who disagree with me, saying the default should be that they are all wheelchair accessible, and the ones that are not wheelchair accessible presumably will be marked "NW."

Which would you prefer in looking at such a meeting schedule?

I think that wheelchair accessible places should have the Wheelchair sign as it's know round the world and non-wheelchair accessible places should have the wheelchair sign with a diagonal line through it. That way it's understandable to all.

no disrespect but being accessable or not isnt by choice, take listed buildings here in the UK, if it is a listed building it doesnt have to be wheelchair accessable if the owner of the building chooses not to have any changes

I do understand that as my husband is a carpenter and has been doing accessible ramps for entry for shops and social buildings (i.e pubs, ect) but all buildings like listed buildings should have a removable ramp that can be put against entrance so wheelchairs can enter the building. My husband's Company he works for has been making a loads of the temporary ramps as we have lots of listed buildings in the County we live in.