The post metadata include publication date; in some themes (list here) they include publication time as well (next to the date). Date and time format are set in Settings > General.
Before the major changes brought about by the implementation of wp 2.7, you could get rid of the time stamp by selecting “Custom” in the settings and typing a space in the box, or the html for a space. Neither of the two works now: so, if the theme you’re using normally displays the time stamp, the only way to get rid of it is type something that will show up next to the date; for instance your nick or your initial (if the metadata don’t include post author – see here), or your city, or a combination of punctuation marks as a decorative element.
You can also paste the html for various symbols (see lists in this or other similar webpages); for example:
☤ for ☤
☉ for ☉
☀ for ☀
☆ for ☆
♬ for ♬
But watch out: some symbols may not show up correctly, or not show up at all, in Explorer. For more on this, see here.