Numbers Stations have been in existence since WW1, these are transmitters that send out strings of numbers, codes, via short wave radio. They are an audio equivalent of a one time pad in many ways.
In the case of the code page, the crossed out line and the two crossed lines as well as the 'flourish' at the base, contain numbers strings.
However with Tibor's last letter, the indented writing close ups show strings of numbers and sometimes letters only in this case they haven't been overwritten by any other agency.
The example below is of an actual numbers station transmission.
You can listen to many more examples of numbers station transmissions on The Conet Project website.
In the case of the code page, the crossed out line and the two crossed lines as well as the 'flourish' at the base, contain numbers strings.
However with Tibor's last letter, the indented writing close ups show strings of numbers and sometimes letters only in this case they haven't been overwritten by any other agency.
The example below is of an actual numbers station transmission.
You can listen to many more examples of numbers station transmissions on The Conet Project website.