Emergency teaching certificates are significant for a variety of reasons.  Different states issue them for different reasons.  Some of the ways in which they are significant include:

They show that it is hard to find qualified teachers for various subject areas.  It is often difficult to find enough good teachers for math and science and special education.  States sometimes have to offer emergency certificates to people who are willing and able to teach in those areas even if they have not completed their teacher training. 

They show that it is hard to find qualified teachers who will teach in certain areas.   These are typically areas where the student bodies are made up largely of children from poor families.  These areas are often hard to teach in and therefore it is hard to find teachers who want to teach there.

They can show that states feel they need more teachers with real world experience.  Some states issue such certificates to people who have significant experience in work that is related to the field in which they wish to teach.  These could be engineers, for example, who would like to come and teach math or science in school.

Thus, the major significance of these certificates is that they show some of the weak spots in our educational system with regard to finding qualified teachers.