"Aamir's letter is short."
Translation:आमिर की चिट्ठी छोटी है।
Your screen is just having problems displaying special conjuncts. I'm guessing you'll also have issues with क्र (क् +र), र्क (र्+क), ड्र (ड्+र), क्ष (क्+ष) and others.
The tick under the letter (called हलन्त ) represents a 'half-letter' that has only the consonant sound without the अ-vowel sound that is it usually comes with (so क=क्+अ). You can write all conjuncts using a हलन्त (for instance न्त in this word can be written as न् त) but this is seldom done outside of learning exercises.