How to create a trigger for multiple schemas?

One of my PostgreSQL databases contains different schemas which share the same structure.

-- schema region_a
CREATE TABLE region_a.point (
gid serial NOT NULL,
geom geometry(point, SRID),
attribute_sample varchar(255),
CONSTRAINT point_pkey PRIMARY KEY (gid)
);

CREATE TABLE region_a.polygon (
gid serial NOT NULL,
geom geometry(polygon, SRID),
attribute varchar(255),
CONSTRAINT polygon_pkey PRIMARY KEY (gid)
);

-- schema region_b
CREATE TABLE region_b.point (
gid serial NOT NULL,
geom geometry(point, SRID),
attribute_sample varchar(255),
CONSTRAINT point_pkey PRIMARY KEY (gid)
);

CREATE TABLE region_b.polygon (
gid serial NOT NULL,
geom geometry(polygon, SRID),
attribute varchar(255),
CONSTRAINT polygon_pkey PRIMARY KEY (gid)
);

-- schema region_c
-- ...

Now I wonder how to create a trigger to add sample points on the polygon features within a schema.

CREATE OR REPLACE FUNCTION sample_attribute_from_polygon()
RETURNS trigger AS $body$
    BEGIN
        NEW.attribute_sample = (SELECT attribute FROM polygon
        WHERE ST_Within(NEW.geom, polygon.geom));
        RETURN NEW;
    END;
$body$ LANGUAGE plpgsql; 

CREATE TRIGGER sample_attribute_from_polygon_tg BEFORE INSERT OR UPDATE
ON point FOR EACH ROW
EXECUTE PROCEDURE sample_attribute_from_polygon();

Is there any way to use the same trigger for all schemas? I’m looking for a solution that’s also working when renaming a schema.