I am sure if you can't prove your identity with a signed message I assume you could do it with the service you offer the engraving
Oh look, what's this?!
-----BEGIN BITCOIN SIGNED MESSAGE-----
My account dArkjON - UID: 132212 has been hacked/lost. The current Timestap is 1498037413 - 06/21/2017 @ 9:30am (UTC).
-----BEGIN BITCOIN SIGNATURE-----
Version: Bitcoin-qt (1.0)
Address: 1DarkjoNMkafK31ATYkQbtp8gg5ymCteja
GxvDve9fNW7DB1AtBf29unERwubgTwWJ2QZGQK6r9oFQLw8ZAj/qDQebcMWQAfDJ/8fpj6dzv13uHPCsEm4KPzE=
-----END BITCOIN SIGNATURE-----
Pro tip: Before commenting, read more than just the OP.