Ship crossing equator finally shows flag (8)
I believe the answer is:
streamer
'flag' is the definition.
(streamer is a kind of flag)
'ship crossing equator finally' is the wordplay.
'ship' becomes 'steamer' (a steam ship).
'crossing' means one lot of letters goes inside another (to cross can mean to go over or around).
'equator finally' becomes 'r' (I can't explain this - if you can you should give a lot more credence to this answer).
'steamer' placed around 'r' is 'STREAMER'.
'shows' is the link.
Can you help me to learn more?
(Other definitions for streamer that I've seen before include "Pennant" , "awful cold?" , "Banner, flag; fishing fly" , "Narrow decorative strip or flag" , "Long strip used at parties" .)