That would make "belief in God" no different than "belief in love," "belief in justice," "belief in guns," and whatever else it is that people profess to believe in. I find this to be a very strange idea. Selfish, egotistically absorbed, unilaterally imposed: to go around claiming one believes in someone, claiming one is acting on that someone's behalf - but all along having no actual connection to that person that would be verified by that person. If God hasn't actually verified one's relationship to Him, one cannot justly claim one has a relationship with God. If theists merely believe in God, but do not necessarily have knowledge of Him, this is like Jane claiming she is married to Peter - while Peter doesn't know anything about this marriage nor are there any legal marriage documents that both Jane and Peter accept as binding.