AABCC - What does AABCC stand for? The Free Dictionary
References in periodicals archive
Polish (with foreign letter V included): natural: AABCC DEEF GHI JKLL MNNOO PQRSS TUV WXYZZZ
variant 2: AABCC DEEF GHI JKLL MNNOO PQRSS TUV WXYZZZ
So, it would be natural to have engraved key labels, such as AABCC, DEEEF ...