I have a similar spider with a white hourglass, except the body is brown rather than black. The biological supply company that provided me with this specimen told me that it was a male black widow. I have been trying to confirm the information that they provided me, so far without overwhelming success. I hope this helps.
I have seen spiders around my home that look identical to the female black widow, only with a white hourglass instead of red. I am not sure what type of spider this is, but I don't think it's a black widow.
I just had one that looked like a black widow with a white hourglass outside my appartment in MD. It had striped legs (white and black), a jet black abdomen and a white hourglass on its back. It was about a cm wide with a big abdomen that came to a point at the end and a very small head. It had an egg sack next to it. This website has a picture of the type of spider I saw: Http://nickjanicki.com/ and they say it is a male widow, but mine had an egg sack. The legs of the one I saw resembled a female's in length and elevation. Its web was very spacious but not very thick. While searching for what type of spider I had, I noticed that some people have seen a black spider with a white hourglass on its back, and some have seen a black spider with an hourglass on its belly. The one on the website has its on its belly, mine had it on its back; what can definitely be assumed, however, is that these are certainly not wolf spiders (as mine was unable to jump, and had a web), or common household or garden spiders (because there are very few references and pics online).
