A blessing is not recited upon performing Mayim Achronim.
 Admur ibid; Michaber 181:7; Rosh Brachos 8:6
 The reason: Those who plan to be Yotzei Birchas Hamazon with another person [and hence only have the 2nd reason applicable to them] do not recite a blessing upon performing Mayim Achronim, as we never recite a blessing for matters performed to avoid danger [1st reason in Admur ibid; Michaber ibid; Bahag Brachos 6] Furthermore, even those who plan on reciting Birchas Hamazon themselves are not accustomed to reciting a blessing, even though ideally a blessing should be recited. The reason for this is because nowadays, we no longer perform Mayim Achronim like it was originally performed and instituted by the Sages, to rub the hands with sweet oils after the washing, and hence we do not recite a blessing. [Admur ibid]