In both incidents, the robbers used physical force to take iPhones and/or iPads.
The first incident occurred near the Monroe Blue Line about 6 a.m. July 16.
The two robbers were described as black males, approximately 19 years of age with dreadlocks and medium complexions.
In the second incident, which occurred near the Clark/Lake Station at 2 p.m. July 18, the robbers were described as two black males between the ages of 19-22.
One robber was described as being about 6 feet tall and weighing 160 pounds with curly hair and medium complexion.
The second robber was said to be 5 feet, 7 inches tall and weighing 160 pounds.
Anyone with information is asked to call the police at 312-747-8380.