Here's a minor issue in the campaign where you can tell what type of ship the blip is by clicking on a blip and seeing if it has subsystems or not. This was done at the start of the match and I hadn't seen either ship yet. Below is a line ship and below that is an escort (the mouse cursor is over each one):
Line
Escort
Tyranid Campaign Can Tell Whether Ships are Escorts or Line Even If Unidentified