"Alonso's thumbs are a symbol, as well as being essential for driving a Formula One car, in that they make a sign of victory and show that everything is under control and well protected," the bank said in a statement.
The Spaniard, winner of the Bahrain season-opener, is third overall after four races.
"The time has come to show who is up for winning the championship and who is not. Now in Europe the moment of truth has arrived for drivers and teams who are going to show who is able to develop quickest," said Alonso.
"A nice fight is starting," he added.
Alonso said he was not worried about his Ferrari engine after suffering a failure in Friday practice at the last race in China.
"I'm sure we will have a great car in Barcelona and I am not worried," he added. "The Ferrari mechanics are very confident that they have resolved the problems and I hope the fans have a fantastic time and there is a great atmosphere as ever."
(Reporting by Alan Baldwin, editing by Justin Palmer)