API:GF GetGuildPostCount

GuildBBSFrame. count=GF_GetGuildPostCount;

Returns
Number - Posts on the message board

Example
/script GuildBBSFrame. count=GF_GetGuildPostCount; /script DEFAULT_CHAT_FRAME:AddMessage(GuildBBSFrame. count)

"Guild Announcements and Message Board" Frame must be opened or it will return 0,