If you put a text between 2 underscores, it just turns it into italic.
If you put a text between 4 stars (2* before and 2* after) it turns it into bold.
The characters you used in your example are shortcuts that format your text, that’s why instead of showing the way you wanted them to, they actually turned the words you typed into italic.
Next time you need to find a player that you see here in the forums, just find one of their posts and click on their name . You will get a popup showing their name in large, and underneath it an underlined link to their Replay profile. If you click on my name for example, you will get replaypoker.com/profile/Maya- which shows you my name on Replay has a hyphen after it that doesn’t show on the forums.
Hope this helps.