Slavic runes definitely existed as people saw it in use with Nordic tribes and copied/modified  and were used more for occasional writing,not for long texts more on jewelry and weapons or buildings. I think I heard of a study being done by Croatian Academy of Science and Art on old Slavic writings. This was done within a study of Croatian decorations;part of it used on our military uniforms (of course this whole work had different background since it was done by a decree of our first president in 1990s). Anyway; as a source of any info it is better than nothing. I will look it up and post some link soon.