I have price series data with open, high, low, close and adjusted close for different companies. I am not sure whether this data is adjusted for stock splits or not and would like to know how to check that.
Only unadjusted data will permit you to see the stock split. You cannot look at adjusted data and tell if a split occurred.
The are a variety of sites that list stock splits (Google: "Stock Split Calendar"). Fidelity provides a reliable one on a monthly basis. You'll have to capture it a month at a time of you want a historical list:
Stock splits makes the company shares more marketable and in this case doesn't affect their seed capital. It's rather book trick. So, first of all you should find a company that have made a split and compare it stock price day before and after that operation. This scenerio should be easy to see because stock splits are make by high-priced company so their market price (per share) after it is rather much lower than before. To be more reliable you can check it through some financial data provider as I mentioned below and compare it to your dataset.
Here's some example.
Apple (AAPL) on 9 June, 2014 made split 7:1, so total shares on market increased (7x times), but price per share was divided by 7. In this example price per share before this event occured was over \$640 and after not much over $90.
If some company make operations like splits, dividends, etc you can check at google / yahoo finance. There also would be a date when that events occured.