I have a pill. I want to know what it is. It is round with a v on one side and the number 4839 on the other

The best advice I can give you is to contact either your local pharmacy or your local emergency room (hospital). Or you can contact your local law enforcement and ask to speak to someone in drug enforcement.

Not knowing where you found this pill or how you came to find it, I would be in error in telling you what this is. I do not know your intent for this pill. The pill needs to be properly disposed of.

Now you can do some searching on your own. Here are some sites:
About - Health & Fitness - Drug Finder (http://gsm.about.com/pid/main.asp)
Common Imprints | Pharmer.org -- Pill Identification Resources (http://www.pharmer.org/imprints)
Pill Identifier - Drugs.com (http://www.drugs.com/pill_identification.html)

Have you tried this?

Pill Identification Wizard (http://www.drugs.com/imprints.php)

We are hesitant to give out drug information without the story behind where and how you found it. You could take it to a local pharmacy for proper identification and disposal if you think that one of your children may be taking it. Or you could just throw it away.