In an exploratory study of mutual intelligibility between the sign languages of the northern part of Belgium (Flemish Sign Language, VGT), the southern part of Belgium (French Belgian Sign Language, LSFB), and the Netherlands (Sign Language of the Netherlands, NGT), we tested the comprehension of VGT by signers of LSFB and NGT. In order to measure the influence of iconic structures (classifier constructions and constructed action) that linguistic analyses have shown to be similar across different sign languages, two genres were compared: narrative and informative signing. To investigate the effect of the overlap between the spoken languages surrounding the Dutch and Flemish Deaf communities, videos were presented in two conditions: first without and subsequently with mouthings. As we hypothesized, both LSFB and NGT signers understood narratives better than informative signing, showing for the first time that iconic structures facilitate comprehension of foreign signing. Furthermore, the results at least partially confirm our hypothesis that NGT signers benefit more from mouthings than LSFB signers, uncovering a source of intelligibility that is unique to sign languages.