@adimehta AddMultiTextColumn
https://www.amibroker.com/guide/afl/addmultitextcolumn.html
And some useful info in the Official Knowledge Base as there is an alternative method to display values that change on bar by bar basis as letters though. Instead of displaying full string we can display single characters in a column using formatChar parameter,
http://www.amibroker.com/kb/2014/12/22/text-output-in-explorations/