[Phanx]

This will check for Moonkin Form when you enter combat, and display a warning message in the Raid Warning Frame if you're not in it.

local name, _, icon = GetSpellInfo(24858)
local message = format("Missing |T%s:20:20:-5|t %s!", icon, name)
local color = { r = 1, g = 1, b = 0 }

local f = CreateFrame("Frame")
f:RegisterEvent("PLAYER_REGEN_DISABLED")
f:SetScript("OnEvent", function(self, event)
	if GetSpecialization() == 1 and GetShapeshiftForm() ~= 5 then
		RaidNotice_AddMessage(RaidWarningFrame, message, color)
	end
end)

Use http://addon.ziuo.net/ to turn that into an addon if you're not sure how.