That's on my "to-do" list. Every member will be able to specify a number of serial numbers (excluding prefixes) that they wish to be alerted for. To reduce the likelihood of misuse, I will probably cap the list at a not-unreasonable number (say 50). Whenever someone else enters a number that is on someone's watch list, an appropriate message will be displayed in blue font after adding the note. The message will likely include the user's username and a suggestion to get in contact with that person via PM to discuss a potential trade.
Of course, the details of this are far from set in stone, so some aspects of the above may change before it is fully implemented. Also, although it's on my to-do list, everything there is done on a "when I have time" basis.
Thanks!
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BWJM, F.O.N.A.
Life Member of CPMS, RCNA, ONA, ANA, IBNS, WCS.
President, IBNS Ontario Chapter.
Treasurer, Waterloo Coin Society.
Show Chair, Cambridge Coin Show.
Fellow of the Ontario Numismatic Association.