In automatic block territory, stop signals shall be of the following types.-
(i) an automatic stop signal which is not dependent upon manual operation but is controlled automatically by the passage of a train into, through and out of the automatic block signalling section;
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(ii) a semi-automatic stop signal which is capable of being operated either as an automatic stop signal or as a manual stop signal, as required;
(a) when a semi-automatic stop signal works as an automatic stop signal, it assumes 'ON' and 'OFF' aspects automatically according to the condition of the automatic block signalling sections ahead;
(b) when a semi-automatic stop signal works as a manual stop signal, it assumes 'ON' aspect automatically on the occupation of the automatic block signalling section ahead but assumes ‘OFF’ aspect when operated manually, provided the relevant automatic block signalling section ahead are clear;
(c) when a semi-automatic stop signal works as an automatic stop signal, the 'A' marker provided under the signal is illuminated and when the 'A' marker is extinguished, the signal shall be deemed to work as a manual stop signal;
(iii) A modified semi-automatic stop signal by converting one of the either automatic or semiautomatic stop signal in mid section under special instructions; when the 'A' marker is extinguished, it works as a modified semi-automatic stop signal and assumes 'off' aspect automatically or is taken 'OFF' in accordance with sub-rule (2) of the rule 105 in case of double line and sub-rule (2) of the rule 107 in case of single line. When 'A' marker is lit it work as any other automatic stop signal;
(iv) a manual stop signal operated manually and which cannot work as an automatic or a semiautomatic stop signal.