An indicator and a fastener and indicator assembly have an inwardly extending engagement portion on the indicator for engaging a complementary portion on the fastener. The fastener may include an annular groove and the indicator may include a complementary annular rim for extending into the annular groove of the fastener. A portion or all of the indicator may be resiliently flexible, and configured so that part or all of the indicator is stretched when in place on the fastener. Examples of fasteners may include nuts and/or bolts.