To see stock price on lock screen in Galaxy S3 you need to enable Swipe as lock screen method. So, you can see information about the price of your portfolio by adding symbols from the stock list. Do as follows:
1. Open "Settings"
2. Tap "Lock Screen"
3. If the screen lock method is Swipe, then you need to tap "Lock Screen Options"
4. Enable "Information Ticker" and tap it
5. Change the content type to Stock" by tapping "contents type"
6. Sliding speed can be changed to Slow, Normal, and Fast
7. Tap "Settings" and then "Auto Refresh" to change the update frequently from every 30 minutes to every 3 hours
8. Tap "Settings" and then "My Stocks" to add up to 20 symbols to your portfolio. You just need to tap the Plus icon and then search for your stock(s)
See Also: How to See Latest News on Lock Screen in Galaxy S3