How can you tell which is traditional Chinese calligraphy and which is simplified Chinese calligraphy?

Unless you read Chinese, you can't.

But, traditional has many more strokes in one character than in simplified. For example, if you wanted to say China in simplified form it's: 中国 while in traditional, it's : 中國。Or, dragon in simplified is:龙 and in traditional: 龍. Traditional is much more complex looking, but it's only recognizable to those who read Chinese.