I am hoping that there may be some particular kanji and/or sounds used in determining if a persons given name is male or female.
There are a number of common suffixes you can use to try to guess. Here is an incomplete list of common suffixes which are a pretty safe bet:
- ko 子
- mi 美
- ka 花・華
- e 江・恵
- na 奈・菜
- no 乃
- ri 里
- rō 郎
- ta 太
- suke 介・助・祐
- o 男・夫・雄・生
- ya 哉・也
- kichi 吉
- hiko 彦
- nobu 信
Also, "girly" kanji—like 愛 "love", 幸 "happiness", 華 "flower", 美 "beauty" etc.—or hiragana will usually indicate a girl's name.
Similarly, "boyish" kanji—like 正 "righteous", 健 "health/strength", 勝 "win", 信 "honesty", etc., will usually indicate a boy's name.
There are many examples where it can be absolutely impossible.
Here are two examples:
雅 - Masa (male name) or Miyabi (female name)
幸 - Kou (male name) or Miyuki (female name)
Outside of the name indicating itself whether it's male or female, I find the easiest way to work it out is doing a Google Image search for that name.
However, I'd advise caution about doing this at work. I have a recollection that sometimes the top results for female names involve women who aren't naked, but aren't wearing much more than their underwear. For an example, try doing "Hitomi" in romaji, even with safe search on.
Some online dictionaries indicate whether a name is male or female, such as jisho.org, though you have to tell it you're specifically after names.
There is a webservice for determine the gender of a name.