Is it important for a Jew to avoid making the letter "t" without the curl on the bottom in order to avoid making a letter that looks like a cross? Is it something that some communities try to avoid but others do without qualms or is it something that all Jews avoid? Is it important enough so that one should correct others (students,children,friends) about it?
Rav Moshe(Igros Moshe YD 1:69) was asked about selling stamps with a cross on it . Rav Moshe brought proof from a Tosfos in Shabbas 149 . He explains that only when the cross is made for the name of the avoda zarah is it an issue. However,when its just for beautification then its no problem. He also mentions that stamps are used in a degraded manner since it gets written on by the post office so that also another point of leinecy.
Writing a lower case t has no relation to the Christian(Catholic) religion it just looks like a cross,so its one step less than an actual cross,from Rav Moshes teshuva its seems there is nothing to worry about.