Dear Xristoforos,
You raise an interesting point!
First of all, not all Lutherans believe that the Pope is the anti-Christ. The Missouri Synod does do that as a matter of policy, but not other synods.
Given the historical circumstances in which this evolved, it really isn't surprising that Lutherans came to believe this. The popes in Luther's time tended not to be the very best of church leaders, let alone Christians.
Let's not forget that a great Catholic servant of God, venerated in Florence and the Dominican Order as a saint, Il Beato Fra Girolamo Savonarola, had issues with Pope Alexander VI and even started a petition addressed to the European rulers to force Alexander to abdicate (which hastened Savonarola's demise). Hopefully, one day all Lutherans will not only drop that calumny against the Bishop of Rome, but will also come into full communion with the Bishop of Rome.
Our Lutheran friend here belongs to a traditional Lutheran movement which has as its goals the deepening of ministerial spirituality and devotional life as well as an openness to resolve the break with the Bishop of Rome, as they say.
They don't see themselves as constituting another denomination within Christianity, but as a reformed Catholic movement. They prefer to call themselves, "Evangelical Catholic" as a result.
The Lutheran-Catholic movement of rapprochement, "Die Sammlung" or "The Gathering" has also published much about what unites Lutherans and Catholics. There are many Lutherans who are as Catholic as any Catholic Christian, such as our Lutheran friend here.
As for the Luther Rose, there is nothing wrong with it at all. There are Lutherans who are about to enter union with Rome via the Ordinariate (the Anglo-Lutheran Catholic Church is one such group) which will keep the Luther Rose, as well as "cultural Lutheranism" afterwards.
Would you suggest that because the Orthodox three-bar Cross is associated with Orthodox who likewise believe the Roman Pope to be an anti-Christ that we shouldn't, as Eastern Catholics, ever use it? Or other similar symbols or saints of the Orthodox Church?
The symbolism of this Rose is meaningful and biblical. As Lutherans restore the broken relationship with Rome, you will be seeing the Rose more and more.
So just please get used to it!

Alex