I think the best thing to do here is to apply the same style as the answer and comment button.
Based on previous posts, I know you are using the SnowFlat theme (and it makes sense because AFAIK it is one of the few themes which don't have texts in the buttons). So the next steps will apply for that specific theme.
1. Edit file qa-theme/SnowFlat/qa-styles.css
2. Add the following code at the end of it:
padding: 0 10px 0 30px;
background-position: 8px center;
3. Edit this line to change the button text