One question about security label command

Greetings,
I got a problem when i used the 'security label on role ...' command to make a label for a database role.
It show me an error like "ERROR: unsupported object type: 1260".So i read the document about 'security label' command ,it show me like this:

SECURITY LABEL [ FOR provider ] ON
{
TABLE object_name |
COLUMN table_name.column_name |
AGGREGATE aggregate_name ( aggregate_signature ) |
DATABASE object_name |
DOMAIN object_name |
EVENT TRIGGER object_name |
FOREIGN TABLE object_name
FUNCTION function_name ( [ [ argmode ] [ argname ] argtype [, ...] ] ) |
LARGE OBJECT large_object_oid |
MATERIALIZED VIEW object_name |
[ PROCEDURAL ] LANGUAGE object_name |
ROLE object_name |
SCHEMA object_name |
SEQUENCE object_name |
TABLESPACE object_name |
TYPE object_name |
VIEW object_name
} IS 'label'

where aggregate_signature is:

* |
[ argmode ] [ argname ] argtype [ , ... ] |
[ [ argmode ] [ argname ] argtype [ , ... ] ] ORDER BY [ argmode ] [ argname ] argtype [ , ... ]

The document show that it can support the object_name named role,so i want to ask what lead to the problem.Thanks.