How to write a bar in a chain programmatically

Consider the function:

Unicode[numericLetters_List]: = StringJoin @ Reverse @ Cases[numericLetters,x_:>If[x!=" ",":"<>x,x]];

now

Unicode[{"06af", "0648", "0644"}]

fingerprints "\: 0644 \: 0648 \: 06af"

instead of ": 0644 : 0648 : 06af"

How can i fix this?