You may notice a student exhibiting one or more of these and decide that something is clearly wrong. Or you may have a "gut-level feeling" that something is amiss. If the latter is the case, don't dismiss your feelings or feel that you need to wait for tangible "proof" that a problem exists. A simple check-in with the student may help you get a better sense of his/her situation.
It is possible that any one of these signs, in and of itself, may simply mean that a student is having an "off" day. Sharing your observations with a friend, a dean, a CAPS therapist or other trusted member of the SU community might provide an opportunity for you to process your feelings and discuss possible options for response.
Please note, any one serious sign (e.g., a student writes a paper expressing hopelessness and/or thoughts of suicide) or a cluster of smaller signs (e.g., emotional outbursts, repeated absence, a noticeable cut on the arm) suggests intervention is required.