The exclamation is simply a notification that you have connected a non-LEGO® sensor into one of the EV3 ports. It does not interfere with the operation of the block.

This warning was removed in LEGO® MINDSTORMS® version 1.1.1.

The Vernier sensor block for EV3 MINDSTORMS can be found here:

LEGO® MINDSTORMS® Education EV3 Core Set with Charger (LEGO-EV3-CORE)
NXT Sensor Adapter (BTA-NXT)
Vernier Engineering Projects with LEGO® MINDSTORMS® Education EV3 (EP-EV3-E)
LEGO® Mindstorms® EV3 Troubleshooting and FAQs