Here are the basic things to look for when trying to determine if you're looking at a scholarly or a popular publication:
Scholarly Journals
Written by and for experts; authoritative
Evaluated by experts; peer-reviewed or refereed
Include bibliographies and/or footnotes
Lengthy articles that contain specialized language
Example: Journal of Social Psychology
Popular publications
Magazines and newspapers
Written by journalists; reviewed by editors
Written for a broad audience
Brief articles that use non-technical language
Contain advertisements, photos, flashy covers
Examples: Time or Newsweek or The New York Times
If, after examining a publication for these features, you still can't tell if it's scholarly/peer-reviewed, search Ulrich's Web (Periodicals Directory) for the publication title.