Look above the bar code on your magazine for an ISSN number. The bar code will usually be on the lower front of the magazine.
Check for an eight-digit number above the bar code. The number will be separated with a hyphen, and an "X" may follow it. The letters "ISSN" should appear before the number.
Look inside the magazine on the Table of Contents page. Look toward the bottom of the page, within the fine print if the ISSN is not found above the bar code.
Search online if the ISSN isn't printed on the magazine's cover or on the Table of Contents page. Go to your favorite search engine and type in the magazine's title followed by "ISSN" to find the ISSN for that particular magazine. Click "Enter" and write down the ISSN number that comes up in the search. Don't click on any of the links unless they have been scanned for viruses and spy ware -- the ISSN should appear in the link text.