Special Features of Banknotes.

Are there any special features introduced in the notes of Mahatma Gandhi series?
The new Mahatma Gandhi series of notes contain several special features vis-à-vis the notes issued earlier. These are:
i) Security thread: Rs.10, Rs.20 and Rs.50 notes contain a readable but fully embedded security windowed security thread. Rs.100, Rs.500 and Rs.1000 notes contain a readable windowed security thread. This thread is partially exposed and partially embedded. When held against light, this thread can be seen as one continuous line. Other than on Rs.1000 notes, this thread contains the words 'Bharat' in the devnagri script and 'RBI' appearing alternately. The security thread of the Rs.1000 note contains the inscription 'Bharat' in the devnagri script, '1000' and 'RBI'. Notes issued earlier have a plain, non-readable fully embedded security thread.
ii) Latent Image: A vertical band behind on the right side of the Mahatma Gandhi’s portrait, which contains a latent image, showing the denominational value 20, 50, 100, 500 or 1000 as the case may be. The value can be seen only when the note is held on the palm and light allowed to fall on it at 45° ; otherwise this feature appears only as a vertical band.
iii) Microletterings: This feature appears between the vertical band and Mahatma Gandhi portrait. It contains the word ‘RBI’ in Rs.10. Notes of Rs.20 and above also contain the denominational value of the notes. This feature can be seen better under a magnifying glass.
iv) Identification mark: A special intaglio feature has been introduced on the left of the watermark window on all notes except Rs.10/- note. This feature is in different shapes for various denominations (Rs.20-Vertical Rectangle, Rs.50-Square, Rs.100-Triangle, Rs.500-Circle, Rs.1000-Diamond) and helps the visually impaired to identify the denomination.
v) Intaglio Printing: The portrait of Mahatma Gandhi, Reserve Bank seal, guarantee and promise clause, Ashoka Pillar Emblem on the left, RBI Governor's signature are printed in intaglio i.e. in raised prints in Rs.20, Rs.50, Rs.100, Rs.500 and Rs.1000 notes.
vi) Fluorescence: The number panels of the notes are printed in fluorescent ink. The notes also have optical fibres. Both can be seen when the notes are exposed to ultra-violet lamp.
vii) Optically Variable Ink: The numeral 500 & 1000 on the Rs.500 [revised colour scheme of mild yellow, mauve and brown] and Rs.1000 notes are printed in Optically Variable Ink viz., a colour-shifting ink. The colour of these numerals appear green when the notes are held flat but would change to blue when the notes are held at an angle.
Forgeries
How does one differentiate between a genuine note and a forged note?
The notes on which the above features are not available can be suspected as forged notes and examined minutely.

From R.B.I. site