Interesting. How would one determine their Mars and Venus signs?
You basically want to find out where your Mars and Venus "was" during the time you were born. Mars and Venus could've have either been in Cancer, Aries, etc.
So to find out where Mars and Venus was during the year you were born click the links and look at the list below. What you want to do is look at the date closest to your birthday.
For example, if someone was born on April 28, 2009 they would need to look and see for the closest date that matches it. By closest, I mean the date right before you were born, not the date after you were born. On the list, the closest date to April 28 would be April 22, 2009. On that day Mars had entered Aries; therefore, they're Mars sign is Aries. If this is male, then that means he's attracted to Aries women.
On April 24, 2009, Venus was in Aries; therefore their Venus is Aries.
Despite this example, as well as for me (where my Venus and Mars are both in Leo), one's Venus and Mars are not always the same.
Here's the list for Mars:http://www.cafeastrology.com/marssignstables.html
Here's the list for Venus:http://www.cafeastrology.com/venussignstables.html
Quick tip: To make your search easier, when you click on the link press Ctrl+F and you'll pull up the search option. Just type in the year you were born and from there look at the month.