Mr Lopez Obrador was "sworn in" by Senator Rosario Ibarra, a human rights activist and member of his party, who placed a red, green and white presidential sash across his shoulders.
Senator Rosario gifted the Mr. Lopez Obrador a sash as his presidential 'swearing in' ceremony. 
It says so in the aritcle. 
( z1 gift :ARG0 ( z2 person :name ( z3 name :op "Rosario" ) :ARG0-of ( z4 have-org-role :ARG2 ( z5 senator ) ) ) :ARG1 ( z6 sash ) :ARG2 ( z7 person :name ( z8 name :op "Mr." :op "Lopez" :op "Obrador" ) ) :time ( z9 ceremony :mod ( z10 swear-in :ARG1 z7 :ARG2 ( z11 have-org-role :ARG0 z7 :ARG2 ( z12 president ) ) ) :poss z7 ) )