My tower in my base is showing a bubble with a picture of a truck and an important sign over it. Does..

Standard Exploration - Construction vehicles can scavenge outside your own base in increments of 4,6,8, or 12 hours. They will collect resources and junk which can be sold for money. Recalling a vehicle early will cost 200 diamonds.

Advanced Exploration - Unlocked at VIP Level 2 for 900,000 VIP Points. Construction vehicles will be sent to another player’s base at random to scavenge for resources and junk. This type of exploration is much more effective and gathers a lot more resources and junk than standard exploration. Be warned, that the “Tower” of the player’s base will alert the player of any invading construction vehicles. The defending player will than have the option to “Snatch” some of the resources and junk that has been gathered by your vehicle. The defending player will then have a cool-down of 2 hours before they can snatch again. Advanced Exploration can only be used a limited amount of times per day.

It means someone is using advanced exploration in your base.