Thanks for the replies, it appeared to me like there was some type of (perhaps very great) impact, due to the cracking and indications in the paint.
As it's not welded, I wouldn't imagine the crack would be able to cross into a tube or the lug, but there seems little to stop it from separating all the way around. The lug itself doesn't seem to be cracked under the paint, with the chrome still intact. However, there does seem to be a smaller crack across the centre of the B, helping to explain the striations emanating from that area on both sides. Hmmm....