What is the white oval pill with L404? I found it in my sons drawe.

The best advice to give you is that you contact either your local pharmacist and ask that person what the drug is and how to properly dispose of it or call your local emergency room and ask there.

If you do not want to do one of those, you can check online at some pharmacology sites and try to identify the pill there.
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)

Do you know for a fact that it is Sine-Off? I have found two sites that say something different. That is why I usually say to contact a professional, such as the local pharmacy.