We present the first results of a campaign aimed at characterising the linear polarisation signals and thus the geometry of binary neutron star mergers (i.e., kilonovae). We carried out the first polarimetric observations of a kilonova called AT 2017gfo, using the FOcal Reducer/low dispersion Spectrograph 2 (FORS2). We predicted for the first time the polarisation signatures expected from kilonovae and highlighted the best strategy to detect linear polarisation in future events. Our studies demonstrate how the detection of polarisation will constrain crucial parameters of these systems, such as the inclination and composition, distribution and extent of the different components of the ejecta.