The Warnings on the Triggers window and Trigger Validation window detects if a trigger returns results to a field and only looks for truncation issues. A lot of variables assign shows as warnings since it treats the variables as 1000 characters by default. Since, the length for the variables is not defined.
To view warnings on triggers, you can select Warnings 
on the Triggers window to display the Trigger Validation window.
If no warnings are detected for the triggers you entered, the message,
0 Warnings Detected, appears. If trigger warnings are detected, they appear in the middle section, and the count is shown. The middle section of the window displays the trigger field, event, conditions, action, and parameter. The
Include Warnings check box is to add the truncation warnings if any to the regular syntax check.
