You can use Japanese langauage characters to do what you want. For example, maru (まる) means circle, and once you write まる using Japanese keyboards it will give some options including this ●. 

But I think it will be difficult to handle that, so the other solution is to copy and paste the symbols from this website: [Special Characters and Symbols][1] and add it in the label expression as:

    '● ' || FieldName

[![enter image description here][2]][2]

Here is the output:

[![enter image description here][3]][3]


  [1]: https://www.hadamitzky.de/english/lp_special_chars.htm
  [2]: https://i.sstatic.net/C4vcD.png
  [3]: https://i.sstatic.net/hP4pR.png