It's six letters long, and uses the letters 'A', 'B', and 'C'.
Use the pointers on the memo to figure out the correct password and open the safe.
1. 'C' cannot appear next to another 'C' or a 'B'.
2. The same letter is never used more than twice.
3. The password reads the same forwards and backwards.
Look at this hint: The password reads the same forwards and backwards.
In other words, since it is a six-letter password, the first three letters and the last three letters are the same, but appear in the reverse order to each other.
The memo states: 'C' cannot appear next to another 'C' or a 'B'.
Or in other words, the only letter that can appear next to a 'C' is an 'A'.
From the first two hints, you know that the first three letters of the password can only be one of the following three possibilities: 'ACA', 'CAA' or 'CAB'.
Since the last three letters are a mirror of the first three, that means there are only three possible password options.
Continuing on from hint three...
The three possible passwords are:
'ACAACA'
'CAAAAC'
'CABBAC'
But the memo states that the same letter cannot be used more than twice.
So only one of the above is a possible answer.
The answer is 'CABBAC'.