So let me take a moment to comment on this. I don't feel demonstrations are the way to go, I don't feel going to the memorial holding a sign or holding signs outside the hall are going to make a lick of difference.
What does make a huge difference, get a large group together. Dress similarly, wear a vast apostate army pin and sit in silence. Don't protest, don't do anything stupid, just sit through the memorial and when it's over leave. Don't sing their songs, don't say amen to their prayer, don't close your eyes, don't fold your hands. When the bread and wine comes around pass it forward essentially looking right through it.
If someone strikes up a conversation with you tell them "I'm here as a member of the Vast Apostate Army". I did it last year, as a single person I literally had an entire congregation in silence around me. This year I'm hoping to get 20 people to do the same thing with me.
That's my thoughts on the thing, you do this as a couple of people holding signs they are going to ignore you. If you go in there as an identity from a group it will make an impact.