Solution 1:

According to this post on steam, this is what you have to use:

Anything enclosed in {} in your Steam Profile name will be interpreted by the game as a symbol. The mana symbols are BWRUG (black, white, red, blue and green respectively). X, 0-9, and k-p (lower-case) are colorless mana costs. Various other letters and punctuation produce other symbols, such as Xbox or PS buttons, arrows, etc.