Manual signs are an augmentative and alternative communication mode which enables and facilitates communication for persons with impairments in speech, language and hearing. There are different ways of teaching signs to persons with intellectual disabilities. One of them is milieu teaching, which is a method where the teaching takes place in natural settings. This method has proven to give good results in generalization and maintenance. Teaching signs to staff in groups has been shown to be effective. The purpose of the present study was to investigate whether sign intervention affected the number of signs and the number of different signs, used by two persons with Down’s syndrome and eleven staff on a day center. The study was carried out as a single-subject design. A sign intervention was conducted at the day center with the two participants with Down’s syndrome. They were educated individually with a procedure inspired by milieu teaching. When the intervention with the two participants was terminated, the staff was educated in a group format. The number of signs and the number of different signs used by the two participants with Down’s syndrome and the staff were registered. The sign intervention with the two participants led to an increased use of signs for one of them and the sign intervention with the staff led to an increased use of signs for the staff together with one of the participants. The main reason for why the sign intervention was effective for one of the two participants with Down’s syndrome and for one group of staff, but not for the other participant or the other group of staff, seems to be that the participants use of signs had an impact on each other. One of the participants with Down’s syndrome and one group of staff seems to have had a positive impact on each others use of signs. The intervention also seems to have been too short and therefore has not given effect for all of the participants.