The plaque depicts three muzzled bear heads, a rampant griffon, and the initials AF and IL, a heraldic composition that has survived the demolition or replacement of its original setting and found a second home in a later structure built centuries afterwards.

The initials belong to Sir Arthur Forbes, who died in 1632, and his wife Janet Lauder, who died sometime after September 1642. Forbes was the original grantee of the land and the builder of what would have been a 17th-century house on the site, part of the broader plantation of Longford in the early 1600s. The plaque almost certainly came from that earlier house, and was re-set in its current position over the gateway when the 19th-century house known as Castle Forbes was developed to the east. Armorial plaques of this kind, bearing a family's heraldic symbols and the initials of husband and wife, were a common way of marking ownership and lineage on the fabric of a building; this one is unusual in having been preserved and deliberately incorporated into later construction rather than lost when the original structure disappeared.